Arduino projects

SYNTHESIS LECTURES ON DIGITAL CIRCUITS AND SYSTEMS

BARRETT

Series ISSN: 1932-3166

Series Editor: Mitchell A. Thornton, Southern Methodist University

Second Edition Steven F. Barrett, University of Wyoming, Laramie This book is about the Arduino microcontroller and the Arduino concept. The visionary Arduino team of Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, and David Mellis launched a new innovation in microcontroller hardware in 2005, the concept of open source hardware. Their approach was to openly share details of microcontroller-based hardware design platforms to stimulate the sharing of ideas and promote innovation. This concept has been popular in the software world for many years. This book is intended for a wide variety of audiences including students of the ﬁne arts, middle and senior high school students, engineering design students, and practicing scientists and engineers. To meet this wide audience, the book has been divided into sections to satisfy the need of each reader. The book contains many software and hardware examples to assist the reader in developing a wide variety of systems. For the examples, the Arduino UNO R3 and the Atmel ATmega328 is employed as the target processor. The second edition has been undated with the latest on the Arduino UNO R3 processor, changes to the Arduino Development Environment and several extended examples.

About SYNTHESIs

Mor gan

& Cl aypool

ISBN: 978-1-60845-859-2

90000

Publishers

w w w. m o r g a n c l a y p o o l . c o m

9 781608 458592

MOR GAN&CL AYPOOL

This volume is a printed version of a work that appears in the Synthesis Digital Library of Engineering and Computer Science. Synthesis Lectures provide concise, original presentations of important research and development topics, published quickly, in digital and print formats. For more information visit www.morganclaypool.com

ARDUINO MICROCONTROLLER: PROCESSING FOR EVERYONE! SECOND EDITION

Arduino Microcontroller: Processing for Everyone!

M &C

Mor gan

&Cl aypool

Publishers

Arduino Microcontroller Processing for Everyone! Second Edition

Steven F. Barrett

SYNTHESIS LECTURES ON DIGITAL CIRCUITS AND SYSTEMS Mitchell A. Thornton, Series Editor

Arduino Microcontroller: Processing for Everyone! Second Edition

Synthesis Lectures on Digital Circuits and Systems Editor Mitchell A. Thornton, Southern Methodist University

The Synthesis Lectures on Digital Circuits and Systems series is comprised of 50- to 100-page books targeted for audience members with a wide-ranging background. The Lectures include topics that are of interest to students, professionals, and researchers in the area of design and analysis of digital circuits and systems. Each Lecture is self-contained and focuses on the background information required to understand the subject matter and practical case studies that illustrate applications. The format of a Lecture is structured such that each will be devoted to a specific topic in digital circuits and systems rather than a larger overview of several topics such as that found in a comprehensive handbook. The Lectures cover both well-established areas as well as newly developed or emerging material in digital circuits and systems design and analysis.

Arduino Microcontroller: Processing for Everyone! Second Edition Steven F. Barrett

2012

Advanced Circuit Simulation Using Multisim Workbench David Báez-López, Félix E. Guerrero-Castro, and Ofelia Delfina Cervantes-Villagómez

2012

Circuit Analysis with Multisim David Báez-López and Félix E. Guerrero-Castro

2011

Microcontroller Programming and Interfacing Texas Instruments MSP430, Part I Steven F. Barrett and Daniel J. Pack

2011

Microcontroller Programming and Interfacing Texas Instruments MSP430, Part II Steven F. Barrett and Daniel J. Pack

2011

Pragmatic Electrical Engineering: Systems and Instruments William Eccles

2011

iii

Pragmatic Electrical Engineering: Fundamentals William Eccles

2011

Introduction to Embedded Systems: Using ANSI C and the Arduino Development Environment David J. Russell

2010

Arduino Microcontroller: Processing for Everyone! Part II Steven F. Barrett

2010

Arduino Microcontroller Processing for Everyone! Part I Steven F. Barrett

2010

Digital System Verification: A Combined Formal Methods and Simulation Framework Lun Li and Mitchell A. Thornton

2010

Progress in Applications of Boolean Functions Tsutomu Sasao and Jon T. Butler

2009

Embedded Systems Design with the Atmel AVR Microcontroller: Part II Steven F. Barrett

2009

Embedded Systems Design with the Atmel AVR Microcontroller: Part I Steven F. Barrett

2009

Embedded Systems Interfacing for Engineers using the Freescale HCS08 Microcontroller II: Digital and Analog Hardware Interfacing Douglas H. Summerville

2009

Designing Asynchronous Circuits using NULL Convention Logic (NCL) Scott C. Smith and JiaDi

2009

Embedded Systems Interfacing for Engineers using the Freescale HCS08 Microcontroller I: Assembly Language Programming Douglas H.Summerville

2009

iv

Developing Embedded Software using DaVinci & OMAP Technology B.I. (Raj) Pawate

2009

Mismatch and Noise in Modern IC Processes Andrew Marshall

2009

Asynchronous Sequential Machine Design and Analysis: A Comprehensive Development of the Design and Analysis of Clock-Independent State Machines and Systems Richard F. Tinder

2009

An Introduction to Logic Circuit Testing Parag K. Lala

2008

Pragmatic Power William J. Eccles

2008

Multiple Valued Logic: Concepts and Representations D. Michael Miller and Mitchell A. Thornton

2007

Finite State Machine Datapath Design, Optimization, and Implementation Justin Davis and Robert Reese

2007

Atmel AVR Microcontroller Primer: Programming and Interfacing Steven F. Barrett and Daniel J. Pack

2007

Pragmatic Logic William J. Eccles

2007

PSpice for Filters and Transmission Lines Paul Tobin

2007

PSpice for Digital Signal Processing Paul Tobin

2007

v

PSpice for Analog Communications Engineering Paul Tobin

2007

PSpice for Digital Communications Engineering Paul Tobin

2007

PSpice for Circuit Theory and Electronic Devices Paul Tobin

2007

Pragmatic Circuits: DC and Time Domain William J. Eccles

2006

Pragmatic Circuits: Frequency Domain William J. Eccles

2006

Pragmatic Circuits: Signals and Filters William J. Eccles

2006

High-Speed Digital System Design Justin Davis

2006

Introduction to Logic Synthesis using Verilog HDL Robert B.Reese and Mitchell A.Thornton

2006

Microcontrollers Fundamentals for Engineers and Scientists Steven F. Barrett and Daniel J. Pack

2006

Copyright © 2012 by Morgan & Claypool

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted in any form or by any means—electronic, mechanical, photocopy, recording, or any other except for brief quotations in printed reviews, without the prior permission of the publisher.

Arduino Microcontroller: Processing for Everyone! Second Edition Steven F. Barrett www.morganclaypool.com

ISBN: 9781608458592 ISBN: 9781608458608

paperback ebook

DOI 10.2200/S00421ED1V01Y201205DCS038

A Publication in the Morgan & Claypool Publishers series SYNTHESIS LECTURES ON DIGITAL CIRCUITS AND SYSTEMS Lecture #38 Series Editor: Mitchell A. Thornton, Southern Methodist University Series ISSN Synthesis Lectures on Digital Circuits and Systems Print 1932-3166 Electronic 1932-3174

Arduino Microcontroller: Processing for Everyone! Second Edition

Steven F. Barrett University of Wyoming, Laramie, WY

SYNTHESIS LECTURES ON DIGITAL CIRCUITS AND SYSTEMS #38

M &C

Morgan

& cLaypool publishers

ABSTRACT This book is about the Arduino microcontroller and the Arduino concept. The visionary Arduino team of Massimo Banzi, David Cuartielles,Tom Igoe, Gianluca Martino, and David Mellis launched a new innovation in microcontroller hardware in 2005, the concept of open source hardware. Their approach was to openly share details of microcontroller-based hardware design platforms to stimulate the sharing of ideas and promote innovation. This concept has been popular in the software world for many years. This book is intended for a wide variety of audiences including students of the fine arts, middle and senior high school students, engineering design students, and practicing scientists and engineers. To meet this wide audience, the book has been divided into sections to satisfy the need of each reader. The book contains many software and hardware examples to assist the reader in developing a wide variety of systems. For the examples, the Arduino UNO R3 and the Atmel ATmega328 is employed as the target processor. The second edition has been undated with the latest on the Arduino UNO R3 processor, changes to the Arduino Development Environment and several extended examples.

KEYWORDS Arduino microcontroller, Arduino UNO R3, Atmel microcontroller, Atmel AVR, ATmega328, microcontroller interfacing, embedded systems design

ix

Contents Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xvii

1

Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 1.2 1.3 1.4

1.5 1.6 1.7 1.8 1.9

1.10 1.11 1.12 1.13

2

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Getting Started . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 Arduino UNO R3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3.1 Arduino host processor — the ATmega328 . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Example: Autonomous Maze Navigating Robot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4.1 Structure chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.4.2 UML activity diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.4.3 Arduino UNO R3 Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Arduino open source schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Other Arduino-based platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Extending the hardware features of the Arduino platform . . . . . . . . . . . . . . . . . . . . . 9 Arduino Software . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 Arduino UNO R3/ATmega328 hardware features . . . . . . . . . . . . . . . . . . . . . . . . . . 13 1.9.1 Memory . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 1.9.2 Port System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 1.9.3 Internal Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Application: Arduino Hardware Studio . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21 Chapter Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 2.1 2.2 2.3

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Big Picture . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Anatomy of a Program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Comments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Include files . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Functions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

23 24 24 26 27 27

x

2.3.4 2.3.5 2.3.6 2.3.7

3

Program constants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interrupt handler definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Main program . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

30 31 31 32

2.4

Fundamental programming concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.1 Operators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.2 Programming constructs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4.3 Decision processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

32 32 36 38

2.5

Arduino Development Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.2 Arduino Development Environment overview . . . . . . . . . . . . . . . . . . . . . . . 2.5.3 Sketchbook concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.5.4 Arduino software, libraries, and language references . . . . . . . . . . . . . . . . . .

41 41 42 42 43

2.6

Application 1: Robot IR sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

2.7

Application 2: Art piece illumination system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

2.8

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

2.9

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

2.10

Chapter Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

Embedded Systems Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3.1

What is an embedded system? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53

3.2

Embedded system design process . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.1 Project Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.2 Background Research . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.3 Pre-Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.4 Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.5 Implement Prototype . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.6 Preliminary Testing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2.7 Complete and Accurate Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.3

Example: Blinky 602A autonomous maze navigating robot system design . . . . . . 59

3.4

Application: Control algorithm for the Blinky 602A Robot . . . . . . . . . . . . . . . . . . 62

3.5

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

3.6

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

3.7


54 54 54 56 56 58 58 59

xi

4

5

Serial Communication Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75 4.1

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 75

4.2

Serial Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.3

Serial Communication Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.4

Serial USART . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 77 4.4.1 System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 78

4.5

System Operation and Programming using Arduino Development Environment features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 82

4.6

System Operation and Programming in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85 4.6.1 Serial Peripheral Interface—SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87

4.7

SPI Programming in the Arduino Development Environment . . . . . . . . . . . . . . . 90

4.8

SPI Programming in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91

4.9

Two-wire Serial Interface—TWI . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92

4.10

Application 1: SD/MMC card module extension via the USART . . . . . . . . . . . . . 92

4.11

Application 2: Programming the Arduino UNO R3 ATmega328 via the ISP . . . 95 4.11.1 Programming Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95

4.12

Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

4.13

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

4.14


Analog to Digital Conversion (ADC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99 5.1

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

5.2

Sampling, Quantization and Encoding . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 100 5.2.1 Resolution and Data Rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

5.3

Analog-to-Digital Conversion (ADC) Process . . . . . . . . . . . . . . . . . . . . . . . . . . . . 103 5.3.1 Transducer Interface Design (TID) Circuit . . . . . . . . . . . . . . . . . . . . . . . . . 104 5.3.2 Operational Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

5.4

ADC Conversion Technologies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 108 5.4.1 Successive-Approximation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109

5.5

The Atmel ATmega328 ADC System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 5.5.1 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111 5.5.2 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 111

5.6

Programming the ADC using the Arduino Development Environment . . . . . . . 114

5.7

Programming the ADC in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

5.8

Example: ADC Rain Gage Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

xii

5.9 5.10

5.11 5.12 5.13 5.14

6

Interrupt Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141 6.1 6.2 6.3 6.4

6.5 6.6

6.7 6.8 6.9

7

5.8.1 ADC Rain Gage Indicator using the Arduino Development Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116 5.8.2 ADC Rain Gage Indicator in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 121 5.8.3 ADC Rain Gage using the Arduino Development Environment—Revisited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 128 One-bit ADC - Threshold Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 129 Digital-to-Analog Conversion (DAC) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 130 5.10.1 DAC with the Arduino Development Environment . . . . . . . . . . . . . . . . . 130 5.10.2 DAC with external converters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 132 5.10.3 Octal Channel, 8-bit DAC via the SPI . . . . . . . . . . . . . . . . . . . . . . . . . . . . 133 Application: Art piece illumination system – Revisited . . . . . . . . . . . . . . . . . . . . . 133 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 137 Chapter Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 138

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ATmega328 Interrupt System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interrupt Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Programming Interrupts in C and the Arduino Development Environment . . . 6.4.1 External Interrupt Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.4.2 Internal Interrupt Programming . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Foreground and Background Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Interrupt Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.1 Real Time Clock in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.6.2 Real Time Clock using the Arduino Development Environment . . . . . . 6.6.3 Interrupt Driven USART in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

141 142 144 144 145 148 153 153 153 156 159 170 170 171

Timing Subsystem . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 173 7.1 7.2

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Timing related terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.1 Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7.2.2 Period . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

173 174 174 174

xiii

7.3 7.4

7.5 7.6

7.7 7.8 7.9 7.10

7.11 7.12 7.13 7.14

8

7.2.3 Duty Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Timing System Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 174 Applications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 178 7.4.1 Input Capture — Measuring External Timing Event . . . . . . . . . . . . . . . . 178 7.4.2 Counting Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 179 7.4.3 Output Compare — Generating Timing Signals to Interface External Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 180 7.4.4 Industrial Implementation Case Study (PWM) . . . . . . . . . . . . . . . . . . . . . 180 Overview of the Atmel ATmega328 Timer System . . . . . . . . . . . . . . . . . . . . . . . . 182 Timer 0 System . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 182 7.6.1 Modes of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 184 7.6.2 Timer 0 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 186 Timer 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 7.7.1 Timer 1 Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 189 Timer 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 193 Programming the Arduino UNO R3 using the built-in Arduino Development Environment Timing Features . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 196 Programming the Timer System in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 7.10.1 Precision Delay in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 198 7.10.2 Pulse Width Modulation in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 200 7.10.3 Input Capture Mode in C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 201 Servo Motor Control with the PWM System in C . . . . . . . . . . . . . . . . . . . . . . . . 203 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 208 Chapter Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 209

Atmel AVR Operating Parameters and Interfacing . . . . . . . . . . . . . . . . . . . . . . . . . 211 8.1 8.2 8.3

8.4

Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Operating Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Battery Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.3.1 Embedded system voltage and current drain specifications . . . . . . . . . . . . 8.3.2 Battery characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Input Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.1 Switches . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.2 Pullup resistors in switch interface circuitry . . . . . . . . . . . . . . . . . . . . . . . . . 8.4.3 Switch Debouncing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

211 212 215 215 215 215 215 217 217

xiv

8.5

8.6 8.7

8.8

8.9 8.10 8.11 8.12

8.13

8.4.4 Keypads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 219 8.4.5 Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 224 8.4.6 LM34 Temperature Sensor Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 Output Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 226 8.5.1 Light Emitting Diodes (LEDs) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 227 8.5.2 Seven Segment LED Displays . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 228 8.5.3 Code Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 230 8.5.4 Tri-state LED Indicator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 231 8.5.5 Dot Matrix Display . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 233 8.5.6 Liquid Crystal Character Display (LCD) in C . . . . . . . . . . . . . . . . . . . . . . 233 8.5.7 Liquid Crystal Character Display (LCD) using the Arduino Development Environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 8.5.8 High Power DC Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 DC Solenoid Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 244 DC Motor Speed and Direction Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 245 8.7.1 DC Motor Operating Parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 246 8.7.2 H-bridge direction control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 247 8.7.3 Servo motor interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 8.7.4 Stepper motor control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 248 8.7.5 AC Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 Interfacing to Miscellaneous Devices . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 8.8.1 Sonalerts, Beepers, Buzzers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 256 8.8.2 Vibrating Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 258 Extended Example 1: Automated Fan Cooling System . . . . . . . . . . . . . . . . . . . . . 258 Extended Example 2: Fine Art Lighting System . . . . . . . . . . . . . . . . . . . . . . . . . . 268 Extended Example 3: Flight Simulator Panel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 272 Extended Example 4: Submersible Robot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 298 8.12.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 299 8.12.2 Structure chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 8.12.3 Circuit Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 300 8.12.4 UML Activity Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 301 8.12.5 Microcontroller Code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 304 8.12.6 Project Extensions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 305 Extended example 5: Weather Station . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 8.13.1 Requirements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 306 8.13.2 Structure chart . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307 8.13.3 Circuit diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 307

xv

8.14 8.15 8.16

8.13.4 UML activity diagrams . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8.13.5 Microcontroller code . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chapter Problems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

308 308 320 320 321

A

ATmega328 Register Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 325

B

ATmega328 Header File . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 329 Author’s Biography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 349 Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 351

Preface This book is about the Arduino microcontroller and the Arduino concept. The visionary Arduino team of Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, and David Mellis launched a new innovation in microcontroller hardware in 2005, the concept of open source hardware. There approach was to openly share details of microcontroller-based hardware design platforms to stimulate the sharing of ideas and innovation. This concept has been popular in the software world for many years. This book is written for a number of audiences. First, in keeping with the Arduino concept, the book is written for practitioners of the arts (design students, artists, photographers, etc.) who may need processing power in a project but do not have an in depth engineering background. Second, the book is written for middle school and senior high school students who may need processing power for a school or science fair project. Third, we write for engineering students who require processing power for their senior design project but do not have the background in microcontroller-based applications commonly taught in electrical and computer engineering curricula. Finally, the book provides practicing scientists and engineers an advanced treatment of the Atmel AVR microcontroller. The second edition has been undated with the latest on the Arduino UNO R3 processor, changes to the Arduino Development Environment and several extended examples.

APPROACH OF THE BOOK To encompass such a wide range of readers, we have divided the book into several portions to address the different readership. Chapters 1 through 2 are intended for novice microcontroller users. Chapter 1 provides a review of the Arduino concept, a description of the Arduino UNO R3 development board, and a brief review of the features of the UNO R3’s host processor, the Atmel ATmega 328 microcontroller. Chapter 2 provides an introduction to programming for the novice programmer. Chapter 2 also introduces the Arduino Development Environment and how to program sketches. It also serves as a good review for the seasoned developer. Chapter 3 provides an introduction to embedded system design processes. It provides a systematic, step-by-step approach on how to design complex systems in a stress free manner. Chapters 4 through 8 provide detailed engineering information on the ATmega328 microcontroller and advanced interfacing techniques. These chapters are intended for engineering students and practicing engineers. However, novice microcontroller users will find the information readable and well supported with numerous examples. The final chapter provides a variety of example applications for a wide variety of skill levels.

xviii

PREFACE

ACKNOWLEDGMENTS A number of people have made this book possible. I would like to thank Massimo Banzi of the Arduino design team for his support and encouragement in writing the book. I would also like to thank Joel Claypool of Morgan & Claypool Publishers who has supported a number of writing projects of Daniel Pack and I over the last several years. He also provided permission to include portions of background information on the Atmel line of AVR microcontrollers in this book from several of our previous projects. I would also like to thank Sparkfun Electronics of Boulder, Colorado; Atmel Incorporated; the Arduino team; and ImageCraft of Palo Alto, California for use of pictures and figures used within the book. I would like to dedicate this book to my close friend and writing partner Dr. Daniel Pack, Ph.D., P.E. Daniel elected to “sit this one out” because of a thriving research program in unmanned aerial vehicles (UAVs). Much of the writing is his from earlier Morgan & Claypool projects. In 2000, Daniel suggested that we might write a book together on microcontrollers. I had always wanted to write a book but I thought that’s what other people did. With Daniel’s encouragement we wrote that first book (and six more since then). Daniel is a good father, good son, good husband, brilliant engineer, a work ethic second to none, and a good friend. To you good friend I dedicate this book. I know that we will do many more together. Finally, I would like to thank my wife and best friend of many years, Cindy.

Laramie, Wyoming, April 2012 Steve Barrett

1

CHAPTER

1

Getting Started Objectives: After reading this chapter, the reader should be able to the following: • Describe the Arduino concept of open source hardware. • Diagram the layout of the Arduino UNO R3 processor board. • Name and describe the different features aboard the Arduino UNO R3 processor board. • Discuss the features and functions of the ATmega328. • List alternate Arduino processing boards. • Describe how to extend the hardware features of the Arduino processor. • Download, configure, and successfully execute a test program using the Arduino software.

1.1

OVERVIEW

Welcome to the world of Arduino! The Arduino concept of open source hardware was developed by the visionary Arduino team of Massimo Banzi, David Cuartilles, Tom Igoe, Gianluca Martino, and David Mellis in Ivrea, Italy. The team’s goal was to develop a line of easy-to-use microcontroller hardware and software such that processing power would be readily available to everyone. In keeping with the Arduino concept, this book is intended for a wide variety of readers. For those wanting a quick exposure to an Arduino microcontroller board and its easy-to-use software, Chapters 1 and 2 are for you. If you need to tap into some of the other features of the processing power of the ATmega328 host microcontroller, Chapters 3 through 8 are for you. Chapter 9 contains a series of extended examples. In keeping with the Arduino open source spirit, you will find a plethora of hardware and software examples throughout the book. I hope you enjoy reading the book, and I also hope you will find it a useful resource in developing Arduino-based projects.

1.2

GETTING STARTED

This chapter is devoted to getting you quickly up and operating with an Arduino-based hardware platform. To get started using an Arduino-based processor, you will need the following hardware and software.

2

1. GETTING STARTED

• an Arduino-based hardware processing platform, • an Arduino compatible power supply, and • the Arduino software. Arduino hardware. Throughout the book, we will be using the Arduino UNO R3 board. A starter’s kit for this platform is available from SparkFun Electronics of Boulder, CO for approximately US$100. The starter kit is illustrated in Figure 1.1. The kit is equipped with the processing board, a USB cable to program the board from a host PC, a small breadboard to prototype external hardware, jumper wires, and many external components. Later in the chapter, we will discuss other Arduinobased processor kits. The UNO R3 board may be purchased separately for US$30.

Figure 1.1: Arduino UNO R3 starter kit. (Used with permission from SparkFun Electronics.)

Power supply. The Arduino processing board may be powered from the USB port during project development. However, it is highly recommended that an external power supply be employed. This will allow developing projects beyond the limited current capability of the USB port. SparkFun Electronics recommends a power supply from 7-12 VDC with a 2.1 mm center positive plug. A power supply of this type is readily available from a number of electronic parts supply companies. For example, the Jameco #133891 power supply is a 9 VDC model rated at 300 mA and equipped with a 2.1 mm center positive plug. It is available for under US$10. Arduino software. You will also need the Arduino software called the Arduino Development Environment. It is available as a free download from the Arduino homepage (www.arduino.cc). In the Application section at the end of this chapter, we describe how to load the software and drivers and get a sample program operating on the Arduino UNO R3 board. In the next several sections, we provide information on the layout and capabilities of the Arduino UNO R3 board and its host the Atmel ATmega328 processor. We also discuss other Arduino-based processing boards and how to extend the features of the Arduino UNO R3 board using the shield concept.

1.3. ARDUINO UNO R3

1.3

ARDUINO UNO R3

The Arduino UNO R3 processing board is illustrated in Figure 1.2. Working clockwise from the left, the board is equipped with a USB connector to allow programming the processor from a host PC. The board may also be programmed using In System Programming (ISP) techniques discussed later in the book. A 6-pin ISP programming connector is on the opposite side of the board from the USB connector.

m M se ria lc om

PW

an al og

re fe re nc e

digital I/O USB-to-serial LED converter TX LED RX LED switch

LED power indicator

USB connector (to PC) ISP programming connector

timebase

power supply connector (7-12 VDC) power supply terminals

analog inputs

Figure 1.2: Arduino UNO R3 layout. (Figure adapted and used with permission of Arduino Team (www. arduino.cc).) (CS-SA-BY ).

The board is equipped with a USB-to-serial converter to allow compatibility between the host PC and the serial communications systems aboard the ATmega328 processor. The UNO R3 is also equipped with several small surface mount LEDs to indicate serial transmission (TX) and reception (RX) and an extra LED for project use. The header strip at the top of the board provides access for an analog reference signal, pulse width modulation (PWM) signals, digital input/output (I/O), and serial communications. The header strip at the bottom of the board provides analog inputs for the analog-to-digital (ADC) system and power supply terminals. Finally, the external power supply connector is provided at the bottom left corner of the board. The top and bottom header strips conveniently mate with an Arduino shield (to be discussed shortly) to extend the features of the host processor.

3

4

1. GETTING STARTED

1.3.1

ARDUINO HOST PROCESSOR — THE ATMEGA328

The host processor for the Arduino UNO R3 is the Atmel Atmega328. The “328” is a 28 pin, 8-bit microcontroller. The architecture is based on the Reduced Instruction Set Computer (RISC) concept which allows the processor to complete 20 million instructions per second (MIPS) when operating at 20 MHz! The “328” is equipped with a wide variety of features as shown in Figure 1.3. The features may be conveniently categorized into the following systems: • Memory system, • Port system, • Timer system, • Analog-to-digital converter (ADC), • Interrupt system, • and the Serial communications.

1.4

EXAMPLE: AUTONOMOUS MAZE NAVIGATING ROBOT

Before taking a more in depth look at the Arduino UNO R3 systems, let’s see how these systems would be used in an application. Graymark (www.graymarkint.com) manufacturers many low-cost, excellent robot platforms. In this example, we will modify the Blinky 602A robot to be controlled by the Arduino UNO R3. The Blinky 602A kit contains the hardware and mechanical parts to construct a line following robot. The processing electronics for the robot consists of analog circuitry. The robot is controlled by two 3 VDC motors which independently drive a left and right wheel. A third non-powered drag wheel provides tripod stability for the robot. In this example, we will equip the Blinky 602A robot platform with three Sharp GP12D IR sensors as shown in Figure 1.4. The robot will be placed in a maze with white reflective walls. The goal is for the robot to detect wall placement and navigate through the maze. (Figure 1.5.) The robot will not be provided any information about the maze. The control algorithm for the robot will be hosted on the Arduino UNO R3.

1.4.1

STRUCTURE CHART

A structure chart is a visual tool used to partition a large project into “doable” smaller parts. It also helps to visualize what systems will be used to control different features of the robot. The arrows within the structure chart indicate the data flow between different portions of the program controlling the robot. The structure chart for the robot project is provided in Figure 1.6. As you

5 1.4. EXAMPLE: AUTONOMOUS MAZE NAVIGATING ROBOT

Memory System - 32K byte, ISP programmable flash - 1K byte, byte addressable EEPROM - 2K byte RAM

Arduino UNO R3

Serial Communications - Serial USART - Serial peripheral interface - Two wire interface (TWI)

Interrupt System - 26 total interrupts - 2 external pin interrupts

Analog-to-digital converter - 6 channel 10-bit ADC (PDIP)

hoste d on the ATme ga 328

Timer System - Two 8-bit timer/counter - One 16-bit timer/counter - Six PWM channels

Port System - 14 digital I/O pins -- 6 provide PWM - 6 analog input pins Figure 1.3: Arduino UNO R3 systems.

6

1. GETTING STARTED

Sharp GP2D12 IR sensor

Center IR sensor Right IR sensor

Left IR sensor Arduino UNO R3

powered wheel

powered wheel

prototype area

turn signals

tripod drag wheel for stability

Figure 1.4: Blinky robot layout.

1.4. EXAMPLE: AUTONOMOUS MAZE NAVIGATING ROBOT

Figure 1.5: Blinky robot navigating maze.

can see, the robot has three main systems: the motor control system, the sensor system, and the digital input/output system. These three systems interact with the main control algorithm to allow the robot to autonomously (by itself ) navigate through the maze by sensing and avoiding walls. determine_robot _action sensor data

robot action

motor_control

desired motor action PWM_left

left motor

PWM_right

right motor

digital

ADC

ch for conv

input/output

conv data

ADC Initialize

ReadADC

left turn signal

left IR sensor

middle IR sensor

right IR sensor

Figure 1.6: Blinky robot structure diagram.

running lights

right turn signal

7

8

1. GETTING STARTED

1.4.2

UML ACTIVITY DIAGRAMS

A Unified Modeling Language (UML) activity diagram, or flow chart, is a tool to help visualize the different steps required for a control algorithm. The UML activity diagram for the robot is provided in Figure 1.7. As you can see, after robot systems are initialized, the robot control system enters a continuous loop to gather data and issue outputs to steer the robot through the maze.

include files global variables function prototypes

initialize ports initialize ADC initialize PWM

while(1)

read sensor outputs (left, middle, right)

determine robot action

issue motor control signals

Figure 1.7: Robot UML activity diagram.

1.5. ARDUINO OPEN SOURCE SCHEMATIC

1.4.3

ARDUINO UNO R3 SYSTEMS

The three IR sensors (left, middle, and right) are mounted on the leading edge of the robot to detect maze walls. The output from the sensors is fed to three ADC channels. The robot motors will each be driven by a pulse width modulation (PWM) channel. The Arduino UNO R3 is interfaced to the motors via a transistor with enough drive capability to handle the maximum current requirements of the motor. The robot will be powered by a 9 VDC battery or a power supply (rated at approximately 2A) which is fed to a 5 VDC voltage regulator. We discuss the details of the interface electronics in a later chapter. From this example, you can see how different systems aboard the Arduino UNO R3 may be used to control different features aboard the Blinky robot. In the next several sections, we present information on the Arduino UNO R3 processor board and software.

1.5

ARDUINO OPEN SOURCE SCHEMATIC

The entire line of Arduino products is based on the visionary concept of open source hardware and software. That is, hardware and software developments are openly shared among users to stimulate new ideas and advance the Arduino concept. In keeping with the Arduino concept, the Arduino team openly shares the schematic of the Arduino UNO R3 processing board. Reference Figure 1.8.

1.6

OTHER ARDUINO-BASED PLATFORMS

There is a wide variety of Arduino-based platforms.The platforms may be purchased from SparkFun Electronics (www.sparkfun.com). Figure 1.9 provides a representative sample. Shown on the left is the Arduino Lily Pad equipped with ATmega328 processor. (The same processor aboard the UNO R3). This processing board can actually be worn and is washable. It was designed to be sewn onto fabric. In the bottom center figure is the Arduino Mega equipped with ATmega2560 processor. This processing board is equipped with 54 digital input/output pins, 14 of the 54 I/O pins may be configured as pulse width modulation pins, 16 analog inputs, and four channels of serial communication capability. In the upper right is the Arduino Mini Stamp. This small, but powerful processing board is equipped with ATmega168 processor.

1.7

EXTENDING THE HARDWARE FEATURES OF THE ARDUINO PLATFORM

Additional features and external hardware may be added to selected Arduino platforms by using a daughter card concept. The daughter card is called an Arduino Shield as shown in Figure 1.10. The shield mates with the header pins on the Arduino board. The shield provides a small fabrication area, a processor reset button, and a general use pushbutton and two light emitting diodes (LEDs).

9

10

1. GETTING STARTED

Figure 1.8: Arduino UNO R3 open source schematic. (Figure adapted and used with permission of the Arduino Team (www.arduino.cc). (CS-SA-BY ). )

1.7. EXTENDING THE HARDWARE FEATURES OF THE ARDUINO PLATFORM

Figure 1.9: Arduino variants. (Used with permission from SparkFun Electronics.)

11

12

1. GETTING STARTED

Figure 1.10: Arduino shield. (Used with permission from SparkFun Electronics.)

This concludes the review of the Arduino UNO R3 and related Arduino-based processing boards. In the next section, we discuss how to download and obtain the latest Arduino software.

1.8. ARDUINO SOFTWARE

1.8

13

ARDUINO SOFTWARE

In the next chapter, we will discuss how to program the Arduino UNO R3 processing board using the Arduino Development Environment. It is essential that you download and get the software operating correctly before proceeding to the next chapter. The Arduino homepage (www.arduino.cc) contains detailed instructions on how to download the software, load the USB drivers, and get a sample program operating on the Arduino UNO R3 processing board. Due to limited space, these instructions will not be duplicated here. The reader is encouraged to visit the Arduino webpage and get the software up and operating at this time. Following the user-friendly instructions provided at the Arduino home page under the “Getting Started” tab, you will have the software downloaded and communicating with your UNO R3 within minutes. This completes a brief overview of the Arduino hardware and software. In the next section, we provide a more detailed overview of the hardware features of the Arduino processor, the Atmel ATmega328.

1.9

ARDUINO UNO R3/ATMEGA328 HARDWARE FEATURES

As previously mentioned, the Arduino UNO R3’s processing power is provided by the ATmega328. The pin out diagram and block diagram for this processor are provided in Figures 1.11 and 1.12. In this section, we provide additional detail on the systems aboard the processor.

Figure 1.11: ATmega328 pin out. (Figure used with permission of Atmel, Incorporated.)

14

1. GETTING STARTED

Figure 1.12: ATmega328 block diagram. (Figure used with permission of Atmel, Incorporated.)

1.9.1

MEMORY

The ATmega328 is equipped with three main memory sections: flash electrically erasable programmable read only memory (EEPROM), static random access memory (SRAM), and byteaddressable EEPROM for data storage. We discuss each memory component in turn.

1.9. ARDUINO UNO R3/ATMEGA328 HARDWARE FEATURES

15

1.9.1.1 In-System Programmable Flash EEPROM

Bulk programmable flash EEPROM is used to store programs. It can be erased and programmed as a single unit. Also, should a program require a large table of constants, it may be included as a global variable within a program and programmed into flash EEPROM with the rest of the program. Flash EEPROM is nonvolatile meaning memory contents are retained when microcontroller power is lost. The ATmega328 is equipped with 32K bytes of onboard reprogrammable flash memory. This memory component is organized into 16K locations with 16 bits at each location. 1.9.1.2 Byte-Addressable EEPROM

Byte-addressable memory is used to permanently store and recall variables during program execution. It too is nonvolatile. It is especially useful for logging system malfunctions and fault data during program execution. It is also useful for storing data that must be retained during a power failure but might need to be changed periodically. Examples where this type of memory is used are found in applications to store system parameters, electronic lock combinations, and automatic garage door electronic unlock sequences. The ATmega328 is equipped with 1024 bytes of EEPROM. 1.9.1.3 Static Random Access Memory (SRAM)

Static RAM memory is volatile. That is, if the microcontroller loses power, the contents of SRAM memory are lost. It can be written to and read from during program execution. The ATmega328 is equipped with 2K bytes of SRAM. A small portion of the SRAM is set aside for the general purpose registers used by the processor and also for the input/output and peripheral subsystems aboard the microcontroller. A complete ATmega328 register listing and accompanying header file is provided in Appendices A and B, respectively. During program execution, RAM is used to store global variables, support dynamic memory allocation of variables, and to provide a location for the stack (to be discussed later).

1.9.2

PORT SYSTEM

The Atmel ATmega328 is equipped with four, 8-bit general purpose, digital input/output (I/O) ports designated PORTB (8 bits, PORTB[7:0]), PORTC (7 bits, PORTC[6:0]), and PORTD (8 bits, PORTD[7:0]). All of these ports also have alternate functions which will be described later. In this section, we concentrate on the basic digital I/O port features. As shown in Figure 1.13, each port has three registers associated with it • Data Register PORTx —- used to write output data to the port. • Data Direction Register DDRx —- used to set a specific port pin to either output (1) or input (0). • Input Pin Address PINx —- used to read input data from the port. Figure 1.13(b) describes the settings required to configure a specific port pin to either input or output. If selected for input, the pin may be selected for either an input pin or to operate in the

16

1. GETTING STARTED

Port x Data Register - PORTx 7 Port x Data Direction Register - DDRx

0

7 Port x Input Pins Address - PINx

0

7

0 a) port associated registers

DDxn

PORTxn

I/O

Comment

Pullup

0

0

input

Tri-state (Hi-Z)

No

0

1

input

source current if externally pulled low

Yes

1

0

output Output Low (Sink)

No

1

1

output Output High (Source)

No

x: port de signa tor (B, C, D) n: pin de signa tor (0 - 7) b) port pin configuration

Figure 1.13: ATmega328 port configuration registers.

high impedance (Hi-Z) mode. In Hi-Z mode, the input appears as high impedance to a particular pin. If selected for output, the pin may be further configured for either logic low or logic high. Port pins are usually configured at the beginning of a program for either input or output and their initial values are then set. Usually all eight pins for a given port are configured simultaneously. We discuss how to configure port pins and how to read/write to them in the next chapter.

1.9.3

INTERNAL SYSTEMS

In this section, we provide a brief overview of the internal features of the ATmega328. It should be emphasized that these features are the internal systems contained within the confines of the micro-

1.9. ARDUINO UNO R3/ATMEGA328 HARDWARE FEATURES

17

controller chip. These built-in features allow complex and sophisticated tasks to be accomplished by the microcontroller. 1.9.3.1 Time Base The microcontroller is a complex synchronous state machine. It responds to program steps in a sequential manner as dictated by a user-written program. The microcontroller sequences through a predictable fetch-decode-execute sequence. Each unique assembly language program instruction issues a series of signals to control the microcontroller hardware to accomplish instruction related operations. The speed at which a microcontroller sequences through these actions is controlled by a precise time base called the clock. The clock source is routed throughout the microcontroller to provide a time base for all peripheral subsystems. The ATmega328 may be clocked internally using a userselectable resistor capacitor (RC) time base or it may be clocked externally. The RC internal time base is selected using programmable fuse bits. You may choose an internal fixed clock operating frequency of 1, 2, 4 or 8 MHz. To provide for a wider range of frequency selections an external time source may be used. The external time sources, in order of increasing accuracy and stability, are an external RC network, a ceramic resonator, or a crystal oscillator. The system designer chooses the time base frequency and clock source device appropriate for the application at hand. 1.9.3.2 Timing Subsystem

The ATmega328 is equipped with a complement of timers which allows the user to generate a precision output signal, measure the characteristics (period, duty cycle, frequency) of an incoming digital signal, or count external events. Specifically, the ATmega328 is equipped with two 8-bit timer/counters and one 16-bit counter. We discuss the operation, programming, and application of the timing system later in the book. 1.9.3.3 Pulse Width Modulation Channels

A pulse width modulated or PWM signal is characterized by a fixed frequency and a varying duty cycle. Duty cycle is the percentage of time a repetitive signal is logic high during the signal period. It may be formally expressed as: duty cycle[%] = (on time/period) × (100%) The ATmega328 is equipped with four pulse width modulation (PWM) channels. The PWM channels coupled with the flexibility of dividing the time base down to different PWM subsystem clock source frequencies allows the user to generate a wide variety of PWM signals: from relatively high frequency low duty cycle signals to relatively low frequency high duty cycle signals.

18

1. GETTING STARTED

PWM signals are used in a wide variety of applications including controlling the position of a servo motor and controlling the speed of a DC motor. We discuss the operation, programming, and application of the PWM system later in the book. 1.9.3.4 Serial Communications The ATmega328 is equipped with a host of different serial communication subsystems including the Universal Synchronous and Asynchronous Serial Receiver and Transmitter (USART), the serial peripheral interface (SPI), and the Two-wire Serial Interface. What all of these systems have in common is the serial transmission of data. In a serial communications transmission, scheme data is sent a single bit at a time from transmitter to receiver.

Serial USART The serial USART may be used for full duplex (two way) communication between a receiver and transmitter. This is accomplished by equipping the ATmega328 with independent hardware for the transmitter and receiver. The USART is typically used for asynchronous communication. That is, there is not a common clock between the transmitter and receiver to keep them synchronized with one another. To maintain synchronization between the transmitter and receiver, framing start and stop bits are used at the beginning and end of each data byte in a transmission sequence. The ATmega328 USART is quite flexible. It has the capability to be set to a variety of data transmission rates known as the Baud (bits per second) rate. The USART may also be set for data bit widths of 5 to 9 bits with one or two stop bits. Furthermore, the ATmega328 is equipped with a hardware generated parity bit (even or odd) and parity check hardware at the receiver. A single parity bit allows for the detection of a single bit error within a byte of data. The USART may also be configured to operate in a synchronous mode. We discuss the operation, programming, and application of the USART later in the book. Serial Peripheral Interface—SPI The ATmega328 Serial Peripheral Interface (SPI) can also be used for two-way serial communication between a transmitter and a receiver. In the SPI system, the transmitter and receiver share a common clock source. This requires an additional clock line between the transmitter and receiver but allows for higher data transmission rates as compared to the USART. The SPI may be viewed as a synchronous 16-bit shift register with an 8-bit half residing in the transmitter and the other 8-bit half residing in the receiver. The transmitter is designated the master since it is providing the synchronizing clock source between the transmitter and the receiver. The receiver is designated as the slave. We discuss the operation, programming, and application of the SPI later in the book. Two-wire Serial Interface—TWI The TWI subsystem allows the system designer to network a number of related devices (microcontrollers, transducers, displays, memory storage, etc.) together into a system using a two wire interconnecting scheme. The TWI allows a maximum of 128 devices to be connected together. Each device has its own unique address and may both transmit and receive

1.10. APPLICATION: ARDUINO HARDWARE STUDIO

19

over the two wire bus at frequencies up to 400 kHz. This allows the device to freely exchange information with other devices in the network within a small area. We discuss the TWI system later in the book. 1.9.3.5 Analog to Digital Converter—ADC The ATmega328 is equipped with an eight channel analog to digital converter (ADC) subsystem. The ADC converts an analog signal from the outside world into a binary representation suitable for use by the microcontroller. The ATmega328 ADC has 10 bit resolution. This means that an analog voltage between 0 and 5 V will be encoded into one of 1024 binary representations between (000)16 and (3F F )16 . This provides the ATmega328 with a voltage resolution of approximately 4.88 mV. We discuss the operation, programming, and application of the ADC later in the book. 1.9.3.6 Interrupts

The normal execution of a program step follows a designated sequence of instructions. However, sometimes this normal sequence of events must be interrupted to respond to high priority faults and status both inside and outside the microcontroller. When these higher priority events occur, the microcontroller must temporarily suspend normal operation and execute event specific actions called an interrupt service routine. Once the higher priority event has been serviced, the microcontroller returns and continues processing the normal program. The ATmega328 is equipped with a complement of 26 interrupt sources.Two of the interrupts are provided for external interrupt sources while the remaining interrupts support the efficient operation of peripheral subsystems aboard the microcontroller. We discuss the operation, programming, and application of the interrupt system later in the book.

1.10 APPLICATION: ARDUINO HARDWARE STUDIO Much like an artist uses a sketch box, we will use an Arduino Hardware Studio throughout the book to develop projects. In keeping with the do-it-yourself (DIY ) spirit of Arduino, we have constructed the Studio using readily available off-the-shelf products as shown in Figure 1.14.The Studio includes the following: • A yellow Pelican Micro Case #1040, • An Arduino UNO R3 evaluation board, • Two Jameco JE21 3.3 x 2.1 inch solderless breadboards and • One piece of black plexiglass. We purposely have not provided any construction details. Instead, we encourage you to use your own imagination to develop and construct your own Arduino Hardware Studio.

20

1. GETTING STARTED

Figure 1.14: Arduino Hardware Studio.

1.11. SUMMARY

21

1.11 SUMMARY In this chapter, we have provided an overview of the Arduino concept of open source hardware. This was followed by a description of the Arduino UNO R3 processor board powered by the ATmega328. An overview of ATmega328 systems followed. We then investigated various processing boards in the Arduino line and concluded with brief guidelines on how to download and run the Arduino software environment.

1.12 REFERENCES • SparkFun Electronics, 6175 Longbow Drive, Suite 200, Boulder, CO 80301 (www.sparkfun.com) • Arduino homepage (www.arduino.cc) • Atmel 8-bit AVR Microcontroller with 4/8/16/32K Bytes In-System Programmable Flash, ATmega48PA, 88PA, 168PA, 328P data sheet: 8171D-AVR-05/11, Atmel Corporation, 2325 Orchard Parkway, San Jose, CA 95131.

1.13 CHAPTER PROBLEMS 1. Describe in your own words the Arduino open source concept. 2. Sketch a block diagram of the ATmega328 and its associated systems. Describe the function of each system. 3. What is the purpose of a structure chart? 4. What is the purpose of a UML activity diagram? 5. Describe the different types of memory components within the ATmega328. Describe applications for each memory type. 6. Describe the three different register types associated with each port. 7. How may the features of the Arduino UNO R3 be extended? 8. Prepare a table of features for different variations of the UNO evaluation board. 9. Prepare a table of features for different Arduino products. 10. Discuss different options for the ATmega328 time base. What are the advantages and disadvantages of each type.

23

CHAPTER

2

Programming Objectives: After reading this chapter, the reader should be able to do the following: • Describe the key components of a program. • Specify the size of different variables within the C programming language. • Define the purpose of the main program. • Explain the importance of using functions within a program. • Write functions that pass parameters and return variables. • Describe the function of a header file. • Discuss different programming constructs used for program control and decision processing. • Describe the key features of the Arduino Development Environment. • Describe what features of the Arduino Development Environment ease the program development process. • List the programming support information available at the Arduino home page. • Write programs for use on the Arduino UNO R3 processing board.

2.1

OVERVIEW

To the novice, programming a microcontroller may appear mysterious, complicated, overwhelming, and difficult. When faced with a new task, one often does not know where to start. The goal of this chapter is to provide a tutorial on how to begin programming. We will use a top-down design approach. We begin with the “big picture” of the chapter followed by an overview of the major pieces of a program. We then discuss the basics of the C programming language. Only the most fundamental concepts will be covered. We then discuss the Arduino Development Environment and how it may be used to develop a program for the Arduino UNO R3 processor board. Throughout the chapter, we provide examples and also provide pointers to a number of excellent references.

24

2. PROGRAMMING

2.2

THE BIG PICTURE

We begin with the big picture of how to program the Arduino UNO R3 as shown in Figure 2.1. This will help provide an overview of how chapter concepts fit together. It also introduces terms used in writing, editing, compiling, loading and executing a program. Most microcontrollers are programmed with some variant of the C programming language. The C programming language provides a nice balance between the programmer’s control of the microcontroller hardware and time efficiency in programming writing. As you can see in Figure 2.1, the compiler software is hosted on a computer separate from the Arduino UNO R3. The job of the compiler is to transform the program provided by the program writer (filename.c and filename.h) into machine code (filename.hex) suitable for loading into the processor. Once the source files (filename.c and filename.h) are provided to the compiler, the compiler executes two steps to render the machine code. The first step is the compilation process. Here the program source files are transformed into assembly code (filename.asm). If the program source files contains syntax errors, the compiler reports these to the user. Syntax errors are reported for incorrect use of the C programming language. An assembly language program is not generated until the syntax errors have been corrected. The assembly language source file (filename.hex) is then passed to the assembler.The assembler transforms the assembly language source file (filename.asm) to machine code (filename.asm) suitable for loading to the Arduino UNO R3. The Arduino Development Environment provides a user friendly interface to aid in program development, transformation to machine code, and loading into the Arduino UNO R3.The Arduino UNO R3 may also be programmed using the In System Programming (ISP) features of the Atmel AVR STK500 (or STK 600) Starter Kit and Development System. We discuss these procedures in a later chapter. In the next section, we will discuss the components of a C program. In a later section, we discuss the user friendly features of the Arduino Development Environment.

2.3

ANATOMY OF A PROGRAM

Programs written for a microcontroller have a fairly repeatable format. Slight variations exist but many follow the format provided. //Comments containing program information // - file name: // - author: // - revision history: // - compiler setting information: // - hardware connection description to microcontroller pins // - program description

2.3. ANATOMY OF A PROGRAM

25

Arduino Development Environment C compiler

filename.c filename.h

compiler filename.asm assembler filename.hex filename.eep

computer Arduino Development Environment

Arduino UNO R3 USB ISP

or C compiler

filename.hex filename.eep

ISP Atmel AVR STK500 Starter Kit and Development System

Figure 2.1: Programming the Arduino UNO R3. (Used with permission from SparkFun Electronics, and Atmel, Incorporated.)

26

2. PROGRAMMING

//include files #include //function prototypes A list of functions and their format used within the program //program constants #define TRUE 1 #define FALSE 0 #define ON 1 #define OFF 0 //interrupt handler definitions Used to link the software to hardware interrupt features //global variables Listing of variables used throughout the program //main program void main(void) { body of the main program } //function definitions A detailed function body and definition for each function used within the program Let’s take a closer look at each piece.

2.3.1

COMMENTS

Comments are used throughout the program to document what and how things were accomplished within a program. The comments help you reconstruct your work at a later time. Imagine that you wrote a program a year ago for a project. You now want to modify that program for a new project. The comments will help you remember the key details of the program.


27

Comments are not compiled into machine code for loading into the microcontroller.Therefore, the comments will not fill up the memory of your microcontroller. Comments are indicated using double slashes (//). Anything from the double slashes to the end of a line is then considered a comment. A multi-line comment can be constructed using a /∗ at the beginning of the comment and a ∗/ at the end of the comment.These are handy to block out portions of code during troubleshooting or providing multi-line comments. At the beginning of the program, comments may be extensive. Comments may include some of the following information: • file name • program author • revision history or a listing of the key changes made to the program • compiler setting information • hardware connection description to microcontroller pins • program description

2.3.2

INCLUDE FILES

Often you need to add extra files to your project besides the main program. For example, most compilers require a “personality file” on the specific microcontroller that you are using. This file is provided with the compiler and provides the name of each register used within the microcontroller. It also provides the link between a specific register’s name within software and the actual register location within hardware. These files are typically called header files and their name ends with a “.h”. Within the C compiler there will also be other header files to include in your program such as the “math.h” file when programming with advanced math functions. To include header files within a program, the following syntax is used: //include files #include #include In an upcoming section, we see how the Arduino Development Environment makes it quite easy to include a header file within a program.

2.3.3

FUNCTIONS

In the next chapter, we discuss in detail the top down design, bottom up implementation approach to designing microcontroller based systems. In this approach, a microcontroller based project including

28

2. PROGRAMMING

both hardware and software is partitioned into systems, subsystems, etc.The idea is to take a complex project and break it into doable pieces with a defined action. We use the same approach when writing computer programs. At the highest level is the main program which calls functions that have a defined action. When a function is called, program control is released from the main program to the function. Once the function is complete, program control reverts back to the main program. Functions may in turn call other functions as shown in Figure 2.2. This approach results in a collection of functions that may be reused over and over again in various projects. Most importantly, the program is now subdivided into doable pieces, each with a defined action. This makes writing the program easier but also makes it much easier to modify the program since every action is in a known location. void main(void) { : function1( );

void function1(void) {

: : } function2( ); : }

void function2(void) { : }

Figure 2.2: Function calling.

There are three different pieces of code required to properly configure and call the function: • the function prototype, • the function call, and • the function body. Function prototypes are provided early in the program as previously shown in the program template. The function prototype provides the name of the function and any variables required by the function and any variable returned by the function. The function prototype follows this format: return_variable function_name(required_variable1, required_variable2);


29

If the function does not require variables or sends back a variable the word “void” is placed in the variable’s position. The function call is the code statement used within a program to execute the function. The function call consists of the function name and the actual arguments required by the function. If the function does not require arguments to be delivered to it for processing, the parenthesis containing the variable list is left empty. The function call follows this format: function_name(required_variable1, required_variable2); A function that requires no variables follows this format: function_name( ); When the function call is executed by the program, program control is transferred to the function, the function is executed, and program control is then returned to the portion of the program that called it. The function body is a self-contained “mini-program.” The first line of the function body contains the same information as the function prototype: the name of the function, any variables required by the function, and any variable returned by the function. The last line of the function contains a “return” statement. Here a variable may be sent back to the portion of the program that called the function. The processing action of the function is contained within the open ({) and close brackets (}). If the function requires any variables within the confines of the function, they are declared next. These variable are referred to as local variables. A local variable is known only within the confines of a specific function. The actions required by the function follow. The function prototype follows this format: return_variable function_name(required_variable1, required_variable2) { //local variables required by the function unsigned int variable1; unsigned char variable2; //program statements required by the function

//return variable return return_variable; } Example: In this example, we describe how to configure the ports of the microcontroller to act as input or output ports. Briefly, associated with each port is a register called the data direction register (DDR). Each bit in the DDR corresponds to a bit in the associated PORT. For example, PORTB has an associated data direction register DDRB. If DDRB[7] is set to a logic 1, the corresponding

30

2. PROGRAMMING

port pin PORTB[7] is configured as an output pin. Similarly, if DDRB[7] is set to logic 0, the corresponding port pin is configured as an input pin. During some of the early steps of a program, a function is called to initialize the ports as input, output, or some combination of both. This is illustrated in Figure 2.3. //function prototypes void initialize_ports(void);

//main function void main(void) { : initialize_ports( ); : }

//function body void initialize_ports(void) { DDRB = 0x00; //initialize PORTB as input PORTB = 0x00; DDRC = 0xFF; PORTC = 0x00;

//initialize PORTC as output //set pins to logic 0

DDRD = 0xFF; PORTD = 0x00; }

//initialize PORTD as output //set pins to logic 0

Figure 2.3: Configuring ports.

2.3.4

PROGRAM CONSTANTS

The #define statement is used to associate a constant name with a numerical value in a program. It can be used to define common constants such as pi. It may also be used to give terms used within a program a numerical value. This makes the code easier to read. For example, the following constants may be defined within a program: //program constants #define TRUE 1 #define FALSE 0 #define ON 1 #define OFF 0


2.3.5

31

INTERRUPT HANDLER DEFINITIONS

Interrupts are functions that are written by the programmer but usually called by a specific hardware event during system operation. We discuss interrupts and how to properly configure them in an upcoming chapter.

2.3.6

VARIABLES

There are two types of variables used within a program: global variables and local variables. A global variable is available and accessible to all portions of the program. Whereas, a local variable is only known and accessible within the function where it is declared. When declaring a variable in C, the number of bits used to store the operator is also specified. In Figure 2.4, we provide a list of common C variable sizes used with the ImageCraft ICC AVR compiler. The size of other variables such as pointers, shorts, longs, etc. are contained in the compiler documentation [ImageCraft]. Size

Range

unsigned char

1

0..255

signed char

1

-128..127

unsigned int

2

0..65535

signed int

2

-32768..32767

float

4

+/-1.175e-38.. +/-3.40e+38

double

4

+/-1.175e-38.. +/-3.40e+38

Type

Figure 2.4: C variable sizes used with the ImageCraft ICC AVR compiler [ImageCraft].

When programming microcontrollers, it is important to know the number of bits used to store the variable and also where the variable will be assigned. For example, assigning the contents of an unsigned char variable, which is stored in 8-bits, to an 8-bit output port will have a predictable result. However, assigning an unsigned int variable, which is stored in 16-bits, to an 8-bit output port does not provide predictable results. It is wise to insure your assignment statements are balanced

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2. PROGRAMMING

for accurate and predictable results. The modifier “unsigned” indicates all bits will be used to specify the magnitude of the argument. Signed variables will use the left most bit to indicate the polarity (±) of the argument. A global variable is declared using the following format provided below. The type of the variable is specified, followed by its name, and an initial value if desired. //global variables unsigned int loop_iterations = 6;

2.3.7

MAIN PROGRAM

The main program is the hub of activity for the entire program. The main program typically consists of program steps and function calls to initialize the processor followed by program steps to collect data from the environment external to the microcontroller, process the data and make decisions, and provide external control signals back to the environment based on the data collected.

2.4

FUNDAMENTAL PROGRAMMING CONCEPTS

In the previous section, we covered many fundamental concepts. In this section we discuss operators, programming constructs, and decision processing constructs to complete our fundamental overview of programming concepts.

2.4.1

OPERATORS

There are a wide variety of operators provided in the C language. An abbreviated list of common operators are provided in Figures 2.5 and 2.6. The operators have been grouped by general category. The symbol, precedence, and brief description of each operator are provided.The precedence column indicates the priority of the operator in a program statement containing multiple operators. Only the fundamental operators are provided. For more information on this topic, see Barrett and Pack in the Reference section at the end of the chapter. 2.4.1.1 General operations Within the general operations category are brackets, parenthesis, and the assignment operator. We have seen in an earlier example how bracket pairs are used to indicate the beginning and end of the main program or a function. They are also used to group statements in programming constructs and decision processing constructs. This is discussed in the next several sections. The parenthesis is used to boost the priority of an operator. For example, in the mathematical expression 7 x 3 + 10, the multiplication operation is performed before the addition since it has a higher precedence. Parenthesis may be used to boost the precedence of the addition operation. If we contain the addition operation within parenthesis 7 x (3 + 10), the addition will be performed before the multiplication operation and yield a different result from the earlier expression.

2.4. FUNDAMENTAL PROGRAMMING CONCEPTS

General Symbol

Precedence

Description

{}

1

Brackets, used to group program statements

()

1

Parenthesis, used to establish precedence

=

12

Assignment Arithmetic Operations

Symbol

Precedence

Description

*

3

Multiplication

/

3

Division

+

4

Addition

-

4

Subtraction Logical Operations

Symbol

Precedence

Description

<

6

Less than

<=

6

Less than or equal to

>

6

Greater

>=

6

Greater than or equal to

== !=

7 7

Equal to Not equal to

&&

9

Logical AND

||

10

Logical OR

Figure 2.5: C operators. (Adapted from [Barrett and Pack]).

33

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2. PROGRAMMING

Bit Manipulation Operations Symbol

Precedence

<<

5

Shift left

>>

5

Shift right

&

8

Bitwise AND

^ |

8 8

Bitwise exclusive OR Bitwise OR

Description

Unary Operations Symbol

Precedence

Description

!

2

Unary negative

~

2

One’s complement (bit-by-bit inversion)

++

2

Increment

-type(argument)

2

Decrement

2

Casting operator (data type conversion)

Figure 2.6: C operators (continued). (Adapted from [Barrett and Pack]).

The assignment operator (=) is used to assign the argument(s) on the right-hand side of an equation to the left-hand side variable. It is important to insure that the left and the right-hand side of the equation have the same type of arguments. If not, unpredictable results may occur. 2.4.1.2 Arithmetic operations The arithmetic operations provide for basic math operations using the various variables described in the previous section. As described in the previous section, the assignment operator (=) is used to assign the argument(s) on the right-hand side of an equation to the left-hand side variable. Example: In this example, a function returns the sum of two unsigned int variables passed to the function.

unsigned int { unsigned int

sum_two(unsigned int variable1, unsigned int variable2) sum;

sum = variable1 + variable2; return sum;


35

}

2.4.1.3 Logical operations

The logical operators provide Boolean logic operations.They can be viewed as comparison operators. One argument is compared against another using the logical operator provided.The result is returned as a logic value of one (1, true, high) or zero (0 false, low). The logical operators are used extensively in program constructs and decision processing operations to be discussed in the next several sections. 2.4.1.4 Bit manipulation operations There are two general types of operations in the bit manipulation category: shifting operations and bitwise operations. Let’s examine several examples: Example: Given the following code segment, what will the value of variable2 be after execution? unsigned char variable1 = 0x73; unsigned char variable2;

variable2 = variable1 << 2; Answer: Variable “variable1” is declared as an eight bit unsigned char and assigned the hexadecimal value of (73)16 . In binary this is (0111_0011)2 . The << 2 operator provides a left shift of the argument by two places. After two left shifts of (73)16 , the result is (cc)16 and will be assigned to the variable “variable2.” Note that the left and right shift operation is equivalent to multiplying and dividing the variable by a power of two. The bitwise operators perform the desired operation on a bit-by-bit basis. That is, the least significant bit of the first argument is bit-wise operated with the least significant bit of the second argument and so on. Example: Given the following code segment, what will the value of variable3 be after execution? unsigned char variable1 = 0x73; unsigned char variable2 = 0xfa; unsigned char variable3; variable3 = variable1 & variable2; Answer: Variable “variable1” is declared as an eight bit unsigned char and assigned the hexadecimal value of (73)16 . In binary, this is (0111_0011)2 . Variable “variable2” is declared as an eight bit unsigned char and assigned the hexadecimal value of (f a)16 . In binary, this is (1111_1010)2 . The bitwise AND operator is specified. After execution variable “variable3,” declared as an eight bit unsigned char, contains the hexadecimal value of (72)16 .

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2. PROGRAMMING

2.4.1.5 Unary operations

The unary operators, as their name implies, require only a single argument. For example, in the following code segment, the value of the variable “i” is incremented. This is a shorthand method of executing the operation “i = i + 1; ” unsigned int

i;

i++; Example: It is not uncommon in embedded system design projects to have every pin on a microcontroller employed. Furthermore, it is not uncommon to have multiple inputs and outputs assigned to the same port but on different port input/output pins. Some compilers support specific pin reference. Another technique that is not compiler specific is bit twiddling. Figure 2.7 provides bit twiddling examples on how individual bits may be manipulated without affecting other bits using bitwise and unary operators.The information provided here was extracted from the ImageCraft ICC AVR compiler documentation [ImageCraft]. Syntax

Description

a|b

bitwise or

a&b

bitwise and

a^b

bitwise exclusive or

PORTA ^= 0x80; // flip bit 7

~a

bitwise complement

PORTA &= ~0x80; // turn off bit 7

Example PORTA |= 0x80; // turn on bit 7 (msb) if ((PINA & 0x81) == 0) // check bit 7 and bit 0

Figure 2.7: Bit twiddling [ImageCraft].

2.4.2

PROGRAMMING CONSTRUCTS

In this section, we discuss several methods of looping through a piece of code. We will examine the “for” and the “while” looping constructs. The for loop provides a mechanism for looping through the same portion of code a fixed number of times. The for loop consists of three main parts: • loop initiation, • loop termination testing, and


37

• the loop increment. In the following code fragment the for loop is executed ten times. unsigned int loop_ctr; for(loop_ctr = 0; loop_ctr < 10; loop_ctr++) { //loop body } The for loop begins with the variable “loop_ctr” equal to 0. During the first pass through the loop, the variable retains this value. During the next pass through the loop, the variable “loop_ctr” is incremented by one. This action continues until the “loop_ctr” variable reaches the value of ten. Since the argument to continue the loop is no longer true, program execution continues after the close bracket for the for loop. In the previous example, the for loop counter was incremented at the beginning of each loop pass. The “loop_ctr” variable can be updated by any amount. For example, in the following code fragment the “loop_ctr” variable is increased by three for every pass of the loop. unsigned int loop_ctr; for(loop_ctr = 0; loop_ctr < 10; loop_ctr=loop_ctr+3) { //loop body } The “loop_ctr” variable may also be initialized at a high value and then decremented at the beginning of each pass of the loop. unsigned int loop_ctr; for(loop_ctr = 10; loop_ctr > 0; loop_ctr--) { //loop body } As before, the “loop_ctr” variable may be decreased by any numerical value as appropriate for the application at hand. The while loop is another programming construct that allows multiple passes through a portion of code. The while loop will continue to execute the statements within the open and close brackets while the condition at the beginning of the loop remains logically true. The code snapshot

38

2. PROGRAMMING

below will implement a ten iteration loop. Note how the “loop_ctr” variable is initialized outside of the loop and incremented within the body of the loop. As before, the variable may be initialized to a greater value and then decremented within the loop body. unsigned int

loop_ctr;

loop_ctr = 0; while(loop_ctr < 10) { //loop body loop_ctr++; } Frequently, within a microcontroller application, the program begins with system initialization actions. Once initialization activities are complete, the processor enters a continuous loop. This may be accomplished using the following code fragment. while(1) {

}

2.4.3

DECISION PROCESSING

There are a variety of constructs that allow decision making. These include the following: • the if statement, • the if–else construct, • the if–else if–else construct, and the • switch statement. The if statement will execute the code between an open and close bracket set should the condition within the if statement be logically true. Example: To help develop the algorithm for steering the Blinky 602A robot through a maze, a light emitting diode (LED) is connected to PORTB pin 1 on the ATmega328. The robot’s center IR sensor is connected to an analog-to-digital converter at PORTC, pin 1. The IR sensor provides a voltage output that is inversely proportional to distance of the sensor from the maze wall. It is desired to illuminate the LED if the robot is within 10 cm of the maze wall. The sensor provides an output voltage of 2.5 VDC at the 10 cm range. The following if statement construct will implement this LED indicator. We provide the actual code to do this later in the chapter.


39

if (PORTC[1] > 2.5) //Center IR sensor voltage greater than 2.5 VDC { PORTB = 0x02; //illuminate LED on PORTB[1] } In the example provided, there is no method to turn off the LED once it is turned on. This will require the else portion of the construct as shown in the next code fragment. if (PORTC[1] > 2.5) //Center IR sensor voltage greater than 2.5 VDC { PORTB = 0x02; //illuminate LED on PORTB[1] } else { PORTB = 0x00; //extinguish the LED on PORTB[1] } The if–else if—else construct may be used to implement a three LED system. In this example, the left, center, and right IR sensors are connected to analog-to-digital converter channels on PORTC pins 2, 1, and 0, respectively. The LED indicators are connected to PORTB pins 2, 1, and 0. The following code fragment implements this LED system. if (PORTC[2] > 2.5) //Left IR sensor voltage greater than 2.5 VDC { PORTB = 0x04; //illuminate LED on PORTB[2] } else if (PORTC[1] > 2.5) //Center IR sensor voltage greater than 2.5 VDC { PORTB = 0x02; //illuminate the LED on PORTB[1] } else if (PORTC[0] > 2.5) //Right IR sensor voltage greater than 2.5 VDC { PORTB = 0x01; //illuminate the LED on PORTB[0] } else //no walls sensed within 10 cm { PORTB = 0x00; //extinguish LEDs }

40

2. PROGRAMMING

The switch statement is used when multiple if-else conditions exist. Each possible condition is specified by a case statement. When a match is found between the switch variable and a specific case entry, the statements associated with the case are executed until a break statement is encountered. Example: Suppose eight pushbutton switches are connected to PORTD. Each switch will implement a different action. A switch statement may be used to process the multiple possible decisions as shown in the following code fragment. void read_new_input(void) { new_PORTD = PIND; if(new_PORTD != old_PORTD) switch(new_PORTD) { case 0x01:

//check for status change PORTD

//process change in PORTD input //PD0 //PD0 related actions

break; case 0x02:

//PD1 //PD1 related actions break;

case 0x04:


case 0x08:


case 0x10:


case 0x20:


case 0x40:

//PD6 //PD6 related actions

2.5. ARDUINO DEVELOPMENT ENVIRONMENT

41

break; case 0x80:

//PD7 //PD7 related actions break; default:;

//all other cases //end switch(new_PORTD) //end if new_PORTD //update PORTD

} } old_PORTD=new_PORTD; } That completes our brief overview of the C programming language. In the next section, we provide an overview of the Arduino Development Environment. You will see how this development tool provides a user-friendly method of quickly developing code applications for the Arduino UNO R3 processing board.

2.5

ARDUINO DEVELOPMENT ENVIRONMENT

In this section, we provide an overview of the Arduino Development Environment (ADE). We begin with some background information about the ADE and then review its user friendly features. We then introduce the sketchbook concept and provide a brief overview of the built-in software features within the ADE. Our goal is to provide a brief introduction to the features. All Arduino related features are well-documented on the Arduino homepage (www.arduino.cc). We will not duplicate this excellent source of material but merely provide pointers to it. In later chapters, we review the different systems aboard the Arduino UNO R3 processing board and show how that system may be controlled using the ADE built-in features.

2.5.1

BACKGROUND

The first version of the Arduino Development Environment was released in August 2005. It was developed at the Interaction Design Institute in Ivrea, Italy to allow students the ability to quickly put processing power to use in a wide variety of projects. Since that time, newer versions incorporating new features, have been released on a regular basis [www.arduino.cc]. At its most fundamental level, the Arduino Development Environment is a user friendly interface to allow one to quickly write, load, and execute code on a microcontroller. A barebones program need only consist of a setup() and loop() function.The Arduino Development Environment adds the other required pieces such as header files and the main program construct. The ADE is written in Java and has its origins in the Processor programming language and the Wiring Project [www.arduino.cc]. In the next several sections, we introduce the user interface and its large collection of user friendly tools. We also provide an overview of the host of built-in C and C++ software functions

42

2. PROGRAMMING

that allows the project developer to quickly put the features of the Arduino UNO R3 processing board to work for them.

2.5.2

ARDUINO DEVELOPMENT ENVIRONMENT OVERVIEW

The Arduino Development Environment is illustrated in Figure 2.8.The ADE contains a text editor, a message area for displaying status, a text console, a tool bar of common functions, and an extensive menuing system. The ADE also provides a user friendly interface to the Arduino UNO R3 which allows for a quick upload of code. This is possible because the Arduino UNO R3 is equipped with a bootloader program. + - sketch_may15a | Arduino 1.0 File Edit Sketch Tools Help

+

sketch_maay15a

Figure 2.8: Arduino Development Environment [www.arduino.cc].

A close up of the Arduino toolbar is provided in Figure 2.9. The toolbar provides single button access to the more commonly used menu features. Most of the features are self explanatory. The “Upload” button compiles your code and uploads it to the Arduino UNO R3. The “Serial Monitor” button opens the serial monitor feature. The serial monitor feature allows text data to be sent to and received from the Arduino UNO R3.

2.5.3

SKETCHBOOK CONCEPT

In keeping with a hardware and software platform for students of the arts, the Arduino environment employs the concept of a sketchbook. An artist maintains their works in progress in a sketchbook. Similarly, we maintain our programs within a sketchbook in the Arduino environment. Furthermore,

2.5. ARDUINO DEVELOPMENT ENVIRONMENT

Verify - checks for errors

Open

Upload

Save +

Creates new sketch

43

Opens serial monitor

Figure 2.9: Arduino Development Environment buttons.

we refer to individual programs as sketches. An individual sketch within the sketchbook may be accessed via the Sketchbook entry under the file tab.

2.5.4

ARDUINO SOFTWARE, LIBRARIES, AND LANGUAGE REFERENCES

The Arduino Development Environment has a number of built in features. Some of the features may be directly accessed via the Arduino Development Environment drop down toolbar illustrated in Figure 2.8. Provided in Figure 2.10 is a handy reference to show all of the available features. The toolbar provides a wide variety of features to compose, compile, load and execute a sketch. We illustrate how to use these features in the Application section later in the chapter. Menu

File - New - Open - Sketchbook - Examples - Close - Save - Save As - Upload - Upload Using Programmer - Page Setup - Print - Preferences - Quit

Edit - Undo - Redo - Cut - Copy - Copy for Forum - Copy as HTML - Paste - Select All - Comment/ Uncomment - Increase Indent - Decrease Indent - Find - Find Next

Sketch - Verify/Compile - Show Sketch Folder - Import Library - Add File

Tools - Auto Format - Archive Sketch - Fix Encoding & Reload - Board - Serial Port - Programmer - Burn Bootloader

Help - Getting Started - Environment - Troubleshooting - Reference - Find in Reference - Frequently Asked Questions - Visit Arduino.cc - About Arduino

Figure 2.10: Arduino Development Environment menu [www.arduino.cc].

Aside from the toolbar accessible features, the Arduino Development Environment contains a number of built-in functions that allow the user to quickly construct a sketch. These built-in

44

2. PROGRAMMING

functions are summarized in Figure 2.11. Complete documentation for these built-in features is available at the Arduino homepage [www.arduino.cc]. This documentation is easily accessible via the Help tab on the Arduino Development Environment toolbar. This documentation will not be repeated here. Instead, we refer to these features at appropriate places throughout the remainder of the book as we discuss related hardware systems. Keep in mind the Arduino open source concept. Users throughout the world are constantly adding new built-in features. As new features are added, they will be released in future Arduino Development Environment versions. As an Arduino user, you too may add to this collection of useful tools. In the next section, we illustrate how to use the Arduino UNO R3 board in several applications.

2.6

APPLICATION 1: ROBOT IR SENSOR

To demonstrate how to construct a sketch in the Arduino Development Environment, we revisit the robot IR sensor application provided earlier in the chapter. We also investigate the sketches’s interaction with the Arduino UNO R3 processing board and external sensors and indicators. We will use the robot project as an ongoing example throughout the remainder of the book. Recall from Chapter 1, the Blinky 602A kit contains the hardware and mechanical parts to construct a line following robot. In this example, we modify the robot platform by equipping it with three Sharp GP12D IR sensors as shown in Figure 2.12. The sensors are available from SparkFun Electronics (www.sparkfun.com). The sensors are mounted to a bracket constructed from thin aluminum. Dimensions for the bracket are provided in the figure. Alternatively, the IR sensors may be mounted to the robot platform using “L” brackets available from a local hardware store. In later Application sections, we equip the robot with all three IR sensors. In this example, we equip the robot with a single sensor and test its function as a proof of concept. The IR sensor provides a voltage output that is inversely proportional to the sensor distance from the maze wall. It is desired to illuminate the LED if the robot is within 10 cm of the maze wall. The sensor provides an output voltage of 2.5 VDC at the 10 cm range. The interface between the IR sensor and the Arduino UNO R3 board is provided in Figure 2.13. The IR sensor’s power (red wire) and ground (black wire) connections are connected to the 5V and Gnd pins on the Arduino UNO R3 board, respectively. The IR sensor’s output connection (yellow wire) is connected to the ANALOG IN 5 pin on the Arduino UNO R3 board. The LED circuit shown in the top right corner of the diagram is connected to the DIGITAL 0 pin on the Arduino UNO R3 board. We discuss the operation of this circuit in the Interfacing chapter later in the book. Earlier in the chapter, we provided a framework for writing the if-else statement to turn the LED on and off. Here is the actual sketch to accomplish this. //************************************************************************* #define LED_PIN 0 //digital pin - LED connection #define IR_sensor_pin 5 //analog pin - IR sensor

SD Card

Firmaton

EEPROM Library - EEPROM clear - EEPROM read - EEPROM write Stepper Library - Motor knob

Ethernet

Analog Input/Output - Analog InOut Serial - Analog Input - Calibration - Fading - Smoothing

Display - LED bar graph - Row column scanning

Digital Input/Output - Blink - Blink without delay - Button - Button state change - Debounce - Tone - Pitch followere - Simple keyboard - Tone 4

Software Serial

SPI - Serial Peripheral Interface

Communication - ASCII Table - Dimmer - Graph - Physical pixel - Virtual color mixer - Serial call response - Serial call response ASCII - Serial input - MIDI Liquid Crystal Display Library - Hello World - Blink - Cursor - Display - Text Direction - Scroll - Serial Input - SetCursor - Autoscroll

Sensors - ADX3xx accelerometer - Knock detector - Memsic2125 two-axis accelerometer - Ping ultrasonic range finder

Servo Library - Knob - Sweep

Control Structures - If statement - For loop - Array - While loop - Switch case - Switch case 2

Arduino Environment Built-in Programs

2.6. APPLICATION 1: ROBOT IR SENSOR

Figure 2.11: Arduino Development Environment built in features [www.arduino.cc].

45

46

2. PROGRAMMING

6 1-7/16

all holes 1/8

1/2

1/2 2

Figure 2.12: Blinky robot platform modified with three IR sensors.

1/2

2.6. APPLICATION 1: ROBOT IR SENSOR 5 VDC 220

10K

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

Arduino UNO R3

5VGnd

2N2222

Ground

ANALOG IN 0 123 4 5

R Y B IR sensor

Figure 2.13: IR sensor interface.

int IR_sensor_value; void setup() { pinMode(LED_PIN, OUTPUT); } void loop() {

//declare variable for IR sensor value

//configure pin 0 for digital output

47

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2. PROGRAMMING

//read analog output from IR sensor IR_sensor_value = analogRead(IR_sensor_pin); if(IR_sensor_value > 512) //0 to 1023 maps to 0 to 5 VDC { digitalWrite(LED_PIN, HIGH); //turn LED on } else { digitalWrite(LED_PIN, LOW); //turn LED off } } //************************************************************************ The sketch begins by providing names for the two Arduino UNO R3 board pins that will be used in the sketch. This is not required but it makes the code easier to read. We define the pin for the LED as “LED_PIN.” Any descriptive name may be used here. Whenever the name is used within the sketch, the number “0” will be substituted for the name by the compiler. After providing the names for pins, the next step is to declare any variables required by the sketch. In this example, the output from the IR sensor will be converted from an analog to a digital value using the built-in Arduino “analogRead” function. A detailed description of the function may be accessed via the Help menu. It is essential to carefully review the support documentation for a built-in Arduino function the first time it is used. The documentation provides details on variables required by the function, variables returned by the function, and an explanation on function operation. The “analogRead” function requires the pin for analog conversion variable passed to it and returns the analog signal read as an integer value (int) from 0 to 1023. So, for this example, we need to declare an integer value to receive the returned value. We have called this integer variable “IR_sensor_value.” Following the declaration of required variables are the two required functions for an Arduino UNO R3 program: setup and loop. The setup function calls an Arduino built-in function, pinMode, to set the “LED_PIN” as an output pin. The loop function calls several functions to read the current analog value on pin 5 (the IR sensor output) and then determine if the reading is above 512 (2.5 VDC). If the reading is above 2.5 VDC, the LED on DIGITAL pin 0 is illuminated, else it is turned off. After completing writing the sketch with the Arduino Development Environment, it must be compiled and then uploaded to the Arduino UNO R3 board.These two steps are accomplished using the “Sketch – Verify/Compile” and the “File – Upload to I/O Board” pull down menu selections. In the next example, we adapt the IR sensor project to provide custom lighting for an art piece.

2.7. APPLICATION 2: ART PIECE ILLUMINATION SYSTEM

2.7

49

APPLICATION 2: ART PIECE ILLUMINATION SYSTEM

My oldest son Jonathan Barrett is a gifted artist (www.ClosertotheSunInternational.com). Although I own several of his pieces, my favorite one is a painting he did during his early student days. The assignment was to paint your favorite place. Jonny painted Lac Laronge, Saskatchewan as viewed through the window of a pontoon plane. Jonny, his younger brother Graham, and I have gone on several fishing trips with friends to this very special location. An image of the painting is provided in Figure 2.14.

Figure 2.14: Lac Laronge, Saskatchewan. Image used with permission, Jonny Barrett, Closer to the Sun Fine Art and Design, Park City, Utah. [www.ClosertotheSunInternational.com]

The circuit and sketch provided in the earlier example may be slightly modified to provide custom lighting for an art piece. The IR sensor could be used to detect the presence and position of those viewing the piece. Custom lighting could then be activated by the Arduino UNO R3 board via the DIGITAL output pins. In the Lac Laronge piece, lighting could be provided from behind the painting using high intensity white LEDs. The intensity of the LEDs could be adjusted by changing

50

2. PROGRAMMING

the value of the resistor is series with the LED. The lighting intensity could also be varied based on the distance the viewer is from the painting. We cover the specifics in an upcoming chapter.

2.8

SUMMARY

The goal of this chapter was to provide a tutorial on how to begin programming. We used a topdown design approach. We began with the “big picture” of the chapter followed by an overview of the major pieces of a program. We then discussed the basics of the C programming language. Only the most fundamental concepts were covered. We then discussed the Arduino Development Environment and how it may be used to develop a program for the Arduino UNO R3 processor board. Throughout the chapter, we provided examples and also provided references to a number of excellent references.

2.9

REFERENCES

• ImageCraft Embedded Systems C Development Tools, 706 Colorado Avenue, #10-88, Palo Alto, CA, 94303, www.imagecraft.com • S. F. Barrett and D.J. Pack, Embedded Systems Design and Applications with the 68HC12 and HCS12, Pearson Prentice Hall, 2005. • Arduino homepage, www.arduino.cc • Jonathan Barrett, Closer to the Sun International. www.ClosertotheSunInternational.com • Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025

2.10 CHAPTER PROBLEMS 1. Describe the steps in writing a sketch and executing it on an Arduino UNO R3 processing board. 2. Describe the key portions of a C program. 3. Describe two different methods to program an Arduino UNO R3 processing board. 4. What is an include file?

2.10. CHAPTER PROBLEMS

51

5. What are the three pieces of code required for a program function? 6. Describe how to define a program constant. 7. Provide the C program statement to set PORTB pins 1 and 7 to logic one. Use bit-twiddling techniques. 8. Provide the C program statement to reset PORTB pins 1 and 7 to logic zero. Use bit-twiddling techniques. 9. What is the difference between a for and while loop? 10. When should a switch statement be used versus the if-then statement construct? 11. What is the serial monitor feature used for in the Arduino Development Environment? 12. Describe what variables are required and returned and the basic function of the following built-in Arduino functions: Blink, Analog Input.

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CHAPTER

3

Embedded Systems Design Objectives: After reading this chapter, the reader should be able to do the following: • Define an embedded system. • List all aspects related to the design of an embedded system. • Provide a step-by-step approach to embedded system design. • Discuss design tools and practices related to embedded systems design. • Apply embedded system design practices in the design of an Arduino-based microcontroller system employing several interacting subsystems. • Provide a detailed design for an autonomous maze navigating robot controlled by the Arduino UNO R3 including hardware layout and interface, structure and UML activity diagrams, and coded algorithm. In Chapters 1 and 2, we provided an overview of the Arduino UNO R3 hardware and the Arduino Development Environment to get you quickly up and operating with this user friendly processor. In the remainder of the book, we will take a second and detailed pass through this information. This chapter provides a step-by-step methodical approach to designing advanced embedded system. Chapters 4 through 7 take an advanced look at the serial communications systems, the analog-todigital converter system, the interrupt system, and the timing system. Chapter 8 provides detailed information on how to interface a wide variety of peripheral devices to the Arduino UNO R3 processor. Throughout these chapters, we show how the built-in features of the Arduino Development Environment may be employed in different applications. In this chapter, we begin with a definition of just what is an embedded system. We then explore the process of how to successfully (and with low stress) develop an embedded system prototype that meets established requirements. We conclude the chapter with an extended example. The example illustrates the embedded system design process in the development and prototype of the autonomous maze navigating robot based on the Blinky 602A (www.graymarkint.com) controlled by the Arduino UNO R3 processing board.

3.1

WHAT IS AN EMBEDDED SYSTEM?

An embedded system contains a microcontroller to accomplish its job of processing system inputs and generating system outputs. The link between system inputs and outputs is provided by a coded

54

3. EMBEDDED SYSTEMS DESIGN

algorithm stored within the processor’s resident memory. What makes embedded systems design so interesting and challenging is the design must also take into account the proper electrical interface for the input and output devices, limited on-chip resources, human interface concepts, the operating environment of the system, cost analysis, related standards, and manufacturing aspects [Anderson]. Through careful application of this material you will be able to design and prototype embedded systems based on the Arduino microcontroller.

3.2

EMBEDDED SYSTEM DESIGN PROCESS

In this section, we provide a step-by-step approach to develop the first prototype of an embedded system that will meet established requirements. There are many formal design processes that we could study. We concentrate on the steps that are common to most. We purposefully avoid formal terminology of a specific approach and instead concentrate on the activities that are accomplished as a system prototype is developed. The design process we describe is illustrated in Figure 3.1 using a Unified Modeling Language (UML) activity diagram. We discuss the UML activity diagrams later in the chapter.

3.2.1

PROJECT DESCRIPTION

The goal of the project description step is to determine what the system is ultimately supposed to do. To achieve this step you must thoroughly investigate what the system is supposed to do. Questions to raise and answer during this step include but are not limited to the following: • What is the system supposed to do? • Where will it be operating and under what conditions? • Are there any restrictions placed on the system design? To answer these questions, the designer interacts with the client to ensure clear agreement on what is to be done. If you are completing this project for yourself, you must still carefully and thoughtfully complete this step. The establishment of clear, definable system requirements may require considerable interaction between the designer and the client. It is essential that both parties agree on system requirements before proceeding further in the design process. The final result of this step is a detailed listing of system requirements and related specifications.

3.2.2

BACKGROUND RESEARCH

Once a detailed list of requirements has been established, the next step is to perform background research related to the design. In this step, the designer will ensure they understand all requirements and features required by the project. This will again involve interaction between the designer and the client.The designer will also investigate applicable codes, guidelines, protocols, and standards related to the project.This is also a good time to start thinking about the interface between different portions

3.2. EMBEDDED SYSTEM DESIGN PROCESS

Project Description - What is the system supposed to do? - Operating conditions and environment - Formal requirements

Background Research - Thoroughly understand desired requirements and features - Determine applicable codes, guidelines, and protocols - Determine interface requirements

Pre-Design - Brainstorm possible solutions - Thoroughly investigate alternatives - Choose best possible solution - Identify specific target microcontroller - Choose a design approach

Employ Design Tools - Structure chart - UML activity diagram - Circuit diagram - Supplemental information

Implement Prototype - Top down versus bottom up - Develop low risk hardware test platform - Software implementation

Preliminary Testing - Develop test plan to insure requirements have been met - Test under anticipated conditions - Test under abusive conditions - Redo testing if errors found - Test in low cost, low risk environment - Full up test

yes

System design need correction? no Complete and Accurate Documentation - System description - Requirements - Structure chart - UML activity diagram - Circuit diagram - Well-documented code - Test plan

Deliver Prototype

Figure 3.1: Embedded system design process.

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of the project particularly the input and output devices peripherally connected to the microcontroller. The ultimate objective of this step is to have a thorough understanding of the project requirements, related project aspects, and any interface challenges within the project.

3.2.3

PRE-DESIGN

The goal of the pre-design step is to convert a thorough understanding of the project into possible design alternatives. Brainstorming is an effective tool in this step. Here, a list of alternatives is developed. Since an embedded system typically involves both hardware and/or software, the designer can investigate whether requirements could be met with a hardware only solution or some combination of hardware and software. Generally, speaking a hardware only solution executes faster; however, the design is fixed once fielded. On the other hand, a software implementation provides flexibility and a typically slower execution speed. Most embedded design solutions will use a combination of both hardware and software to capitalize on the inherent advantages of each. Once a design alternative has been selected, the general partition between hardware and software can be determined. It is also an appropriate time to select a specific hardware device to implement the prototype design. If a microcontroller technology has been chosen, it is now time to select a specific controller. This is accomplished by answering the following questions: • What microcontroller systems or features i.e., ADC, PWM, timer, etc.) are required by the design? • How many input and output pins are required by the design? • What is the maximum anticipated operating speed of the microcontroller expected to be? Recall from Chapter 1 there are a wide variety of Arduino-based microcontrollers available to the designer.

3.2.4

DESIGN

With a clear view of system requirements and features, a general partition determined between hardware and software, and a specific microcontroller chosen, it is now time to tackle the actual design. It is important to follow a systematic and disciplined approach to design. This will allow for low stress development of a documented design solution that meets requirements. In the design step, several tools are employed to ease the design process. They include the following: • Employing a top-down design, bottom up implementation approach, • Using a structure chart to assist in partitioning the system, • Using a Unified Modeling Language (UML) activity diagram to work out program flow, and • Developing a detailed circuit diagram of the entire system.

3.2. EMBEDDED SYSTEM DESIGN PROCESS

57

Let’s take a closer look at each of these. The information provided here is an abbreviated version of the one provided in “Microcontrollers Fundamentals for Engineers and Scientists.” The interested reader is referred there for additional details and an indepth example [Barrett and Pack]. Top down design, bottom up implementation. An effective tool to start partitioning the design is based on the techniques of top-down design, bottom-up implementation. In this approach, you start with the overall system and begin to partition it into subsystems. At this point of the design, you are not concerned with how the design will be accomplished but how the different pieces of the project will fit together. A handy tool to use at this design stage is the structure chart. The structure chart shows the hierarchy of how system hardware and software components will interact and interface with one another. You should continue partitioning system activity until each subsystem in the structure chart has a single definable function. UML Activity Diagram. Once the system has been partitioned into pieces, the next step in the design process is to start working out the details of the operation of each subsystem we previously identified. Rather than beginning to code each subsystem as a function, we will work out the information and control flow of each subsystem using another design tool: the Unified Modeling Language (UML) activity diagram. The activity diagram is simply a UML compliant flow chart. UML is a standardized method of documenting systems. The activity diagram is one of the many tools available from UML to document system design and operation. The basic symbols used in a UML activity diagram for a microcontroller based system are provided in Figure 3.2[Fowler].

Starting Activity

Branch

Transfer of Control

Final State

Action State

Figure 3.2: UML activity diagram symbols. Adapted from [Fowler].

58


To develop the UML activity diagram for the system, we can use a top-down, bottom-up, or a hybrid approach. In the top-down approach, we begin by modeling the overall flow of the algorithm from a high level. If we choose to use the bottom-up approach, we would begin at the bottom of the structure chart and choose a subsystem for flow modeling. The specific course of action chosen depends on project specifics. Often, a combination of both techniques, a hybrid approach, is used. You should work out all algorithm details at the UML activity diagram level prior to coding any software. If you can not explain system operation at this higher level, first, you have no business being down in the detail of developing the code. Therefore, the UML activity diagram should be of sufficient detail so you can code the algorithm directly from it [Dale]. In the design step, a detailed circuit diagram of the entire system is developed. It will serve as a roadmap to implement the system. It is also a good idea at this point to investigate available design information relative to the project. This would include hardware design examples, software code examples, and application notes available from manufacturers. At the completion of this step, the prototype design is ready for implementation and testing.

3.2.5

IMPLEMENT PROTOTYPE

To successfully implement a prototype, an incremental approach should be followed. Again, the topdown design, bottom-up implementation provides a solid guide for system implementation. In an embedded system design involving both hardware and software, the hardware system including the microcontroller should be assembled first. This provides the software the required signals to interact with. As the hardware prototype is assembled on a prototype board, each component is tested for proper operation as it is brought online. This allows the designer to pinpoint malfunctions as they occur. Once the hardware prototype is assembled, coding may commence. As before, software should be incrementally brought online. You may use a top down, bottom up, or hybrid approach depending on the nature of the software. The important point is to bring the software online incrementally such that issues can be identified and corrected early on. It is highly recommended that low cost stand-in components be used when testing the software with the hardware components. For example, push buttons, potentiometers, and LEDs may be used as low cost stand-in component simulators for expensive input instrumentation devices and expensive output devices such as motors. This allows you to insure the software is properly operating before using it to control the actual components.

3.2.6

PRELIMINARY TESTING

To test the system, a detailed test plan must be developed. Tests should be developed to verify that the system meets all of its requirements and also intended system performance in an operational environment.The test plan should also include scenarios in which the system is used in an unintended manner. As before a top-down, bottom-up, or hybrid approach can be used to test the system.

3.3. EXAMPLE: BLINKY 602A AUTONOMOUS MAZE NAVIGATING ROBOT SYSTEM DESIGN

Once the test plan is completed, actual testing may commence. The results of each test should be carefully documented. As you go through the test plan, you will probably uncover a number of run time errors in your algorithm. After you correct a run time error, the entire test plan must be performed again. This ensures that the new fix does not have an unintended affect on another part of the system. Also, as you process through the test plan, you will probably think of other tests that were not included in the original test document. These tests should be added to the test plan. As you go through testing, realize your final system is only as good as the test plan that supports it! Once testing is complete, you might try another level of testing where you intentionally try to “jam up” the system. In another words, try to get your system to fail by trying combinations of inputs that were not part of the original design. A robust system should continue to operate correctly in this type of an abusive environment. It is imperative that you design robustness into your system. When testing on a low cost simulator is complete, the entire test plan should be performed again with the actual system hardware. Once this is completed you should have a system that meets its requirements!

3.2.7

COMPLETE AND ACCURATE DOCUMENTATION

With testing complete, the system design should be thoroughly documented. Much of the documentation will have already been accomplished during system development. Documentation will include the system description, system requirements, the structure chart, the UML activity diagrams documenting program flow, the test plan, results of the test plan, system schematics, and properly documented code. To properly document code, you should carefully comment all functions describing their operation, inputs, and outputs. Also, comments should be included within the body of the function describing key portions of the code. Enough detail should be provided such that code operation is obvious. It is also extremely helpful to provide variables and functions within your code names that describe their intended use. You might think that a comprehensive system documentation is not worth the time or effort to complete it. Complete documentation pays rich dividends when it is time to modify, repair, or update an existing system. Also, well-documented code may be often reused in other projects: a method for efficient and timely development of new systems.

3.3

EXAMPLE: BLINKY 602A AUTONOMOUS MAZE NAVIGATING ROBOT SYSTEM DESIGN

To illustrate the design process, we provide an in depth example using the Blinky 602A robot manufactured by Graymark (www.graymarkint.com). In the upcoming paragraphs, we progress through the design process a step at a time. Problem description and background research. Graymark manufacturers many low-cost, excellent robot platforms. In this project, we will modify the Blinky 602A robot to be controlled by an Arduino UNO R3 processing board. The Blinky 602A kit contains the hardware and mechanical

59

60


parts to construct a line following robot. The processing electronics for the robot consists of analog circuitry. The robot is controlled by two 3 VDC motors, which independently drive a left and right wheel. A third non-powered drag wheel provides tripod stability for the robot. In this project, we replace the analog control circuitry with the Arduino UNO R3 as the processing element. We also modify the robot’s mission from being a line follower to autonomous maze navigator. To detect maze walls, we equip the Blinky 602A robot platform with three Sharp GP12D IR sensors as shown in Figure 3.3. The robot will be placed in a maze with reflective white walls. The goal of the project is for the robot to detect maze walls and navigate through the maze without touching the walls. The robot will not be provided any information about the maze. It must gather maze information on its own as it progresses through the maze. The control algorithm for the robot will be hosted on the Arduino UNO R3 processing board. Requirements: The requirements for this project are straight forward; the robot will autonomously (on its own) navigate through the maze without touching maze walls. It is important to note that a map of the maze will not be programmed into the robot. The robot will sense the presence of the maze walls using the Sharp IR sensors and then make decisions to avoid the walls and process through the maze. From this description, the following requirements result. The robot will be: • Equipped with three Sharp IR sensors to sense maze walls. • Propelled through the maze using the two powered wheels provided in the Blinky 602A kit and a third drag wheel for stability. • Controlled by the Arduino UNO R3 processing board. • Equipped with turn signals (LEDs) to indicate a turn. • Equipped with LEDs, one for each IR sensor, to indicate a wall has been detected by a specific sensor. Pre-design. With requirements clearly understood, the next step is normally to brainstorm possible solutions. In this example, we have already decided to use the Arduino UNO R3 processing board. Other alternatives include using analog or digital hardware to determine robot action or another microcontroller. Circuit diagram. The circuit diagram for the robot is provided in Figure 3.4. The three IR sensors (left, middle, and right) will be mounted on the leading edge of the robot to detect maze walls. The output from the sensors is fed to three Arduino UNO R3 ADC channels (ANALOG IN 0-2). The robot motors will be driven by PWM channels (PWM: DIGITAL 11 and PWM: DIGITAL 10). The Arduino UNO R3 is interfaced to the motors via a transistor (2N2222) with enough drive capability to handle the maximum current requirements of the motor. Since the microcontroller is powered at 5 VDC and the motors are rated at 3 VDC, two 1N4001 diodes are placed in series with the motor. This reduces the supply voltage to the motor to be approximately 3 VDC. The robot

3.3. EXAMPLE: BLINKY 602A AUTONOMOUS MAZE NAVIGATING ROBOT SYSTEM DESIGN

ANALOG IN 0 123 4 5 5VGnd

Arduino UNO R3

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

Sharp GP2D12 IR sensor

wall detected LEDs

prototype area

turn signals Figure 3.3: Robot layout with the Arduino UNO R3 processing board.

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will be powered by a 9 VDC battery which is fed to a 5 VDC voltage regulator. The details of the interface electronics are provided in a later chapter. To save on battery expense, it is recommended to use a 9 VDC, 2A rated inexpensive, wall-mount power supply to provide power to the 5 VDC voltage regulator. A power umbilical of braided wire may be used to provide power to the robot while navigating about the maze. Structure chart: The structure chart for the robot project is provided in Figure 3.5. UML activity diagrams: The UML activity diagram for the robot is provided in Figure 3.6. Arduino UNO R3 Program: We will develop the entire control algorithm for the Arduino UNO R3 board in the Application sections in the remainder of the book. We get started on the control algorithm in the next section.

3.4

APPLICATION: CONTROL ALGORITHM FOR THE BLINKY 602A ROBOT

In this section, we provide the basic framework for the robot control algorithm.The control algorithm will read the IR sensors attached to the Arduino UNO R3 ANALOG IN (pins 0 – 2). In response to the wall placement detected, it will render signals to turn the robot to avoid the maze walls. Provided in Figure 3.7 is a truth table that shows all possibilities of maze placement that the robot might encounter. A detected wall is represented with a logic one. An asserted motor action is also represented with a logic one. The robot motors may only be moved in the forward direction. We review techniques to provide bi-directional motor control in an upcoming chapter. To render a left turn, the left motor is stopped and the right motor is asserted until the robot completes the turn. To render a right turn, the opposite action is required. The task in writing the control algorithm is to take the UML activity diagram provided in Figure 3.6 and the actions specified in the robot action truth table (Figure 3.7 and transform both into an Arduino sketch. This may seem formidable but we take it a step at a time. The sketch written in the Applications section of the previous chapter will serve as our starting point. The control algorithm begins with Arduino UNO R3 pin definitions. Variables are then declared for the readings from the three IR sensors. The two required Arduino functions follow: setup() and loop(). In the setup() function, Arduino UNO R3 pins are declared as output. The loop() begins by reading the current value of the three IR sensors. Recall from the Application section in the previous chapter, the 512 value corresponds to a particular IR sensor range. This value may be adjusted to change the range at which the maze wall is detected. The read of the IR sensors is followed by an eight part if-else if statement. The statement contains a part for each row of the truth table provided in Figure 3.7. For a given configuration of sensed walls, the appropriate wall detection LEDs are illuminated followed by commands to activate the motors (analogWrite) and illuminate the appropriate turn signals. The analogWrite command issues a signal from 0 to 5 VDC by sending a constant from 0 to 255 using pulse width modulation (PWM) techniques. PWM techniques will be discussed in an upcoming chapter. The turn signal commands provide to actions: the appropriate

Figure 3.4: Robot circuit diagram. D2

1N4001

-

M

+

10K

left turn signal

A0

D11

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

5 VDC

2N2222 D3

10K

2N2222

10K

2N2222

220

220

220 wall left

5 VDC

wall center

A1

5 VDC

D4

Arduino UNO R3

5 VDC

left motor/wheel interface

240

3 VDC at 100 mA

1N4001

1N4001

2N2222

5 VDC

5 VDC

IR sensor middle

D5

240

voltage dropping diodes

A2

wall right 10K

2N2222

220

5 VDC

D6

-

M

+

10K

right turn signal

2N2222

male header pins

right motor/wheel interface

D10

5 VDC

IR sensor right

ANALOG IN 0 123 4 5 5VGnd

IR sensor left

2N2222

220

5 VDC

motor current

3 VDC at 100 mA

1N4001

1N4001

5 VDC

1N4001 protection diode

Sensor connection: - Red: 5 VDC - Yellow: Signal output - Black: Ground

3.4. APPLICATION: CONTROL ALGORITHM FOR THE BLINKY 602A ROBOT 63

64


determine_robot _action sensor data

robot action

motor_control

desired motor action PWM_left

left motor

digital

ADC

ch for conv

PWM_right

right motor

input/output

conv data

ADC Initialize

ReadADC

left turn signal

left IR sensor

middle IR sensor

right IR sensor

wall detect LEDS

right turn signal

Figure 3.5: Robot structure diagram.

turns signals are flashed and a 1.5 s total delay is provided. This provides the robot 1.5 s to render a turn. This delay may need to be adjusted during the testing phase. //************************************************************************* //analog input pins #define left_IR_sensor 0 //analog pin - left IR sensor #define center_IR_sensor 1 #define right_IR_sensor 2

//analog pin - center IR sensor //analog pin - right IR sensor

#define wall_left #define wall_center #define wall_right

3 4 5

//digital output pins //LED indicators - wall detectors //digital pin - wall_left //digital pin - wall_center //digital pin - wall_right

#define left_turn_signal

2

//LED indicators - turn signals //digital pin - left_turn_signal

3.4. APPLICATION: CONTROL ALGORITHM FOR THE BLINKY 602A ROBOT


initialize ports initialize ADC initialize PWM

while(1)

setup() - configure pins for output define global variables

loop() read sensor outputs (left, middle, right)


illuminate LEDs - wall detected


illuminate LEDs - turn signals

delay

a) UML for C programming Figure 3.6: Robot UML activity diagram.

read sensor outputs (left, middle, right)


illuminate LEDs - wall detected


illuminate LEDs - turn signals - delay

b) UML for Arduino programming

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Left Middle Right Wall Wall Wall Left Right Left Right Sensor Sensor Sensor Left Middle Right Motor Motor Signal Signal 0 1 2 3 4 5 6 7

0 0 0 0 1 1 1 1

0 0 1 1 0 0 1 1

0 1 0 1 0 1 0 1

0 0 0 0 1 1 1 1

0 0 1 1 0 0 1 1

0 1 0 1 0 1 0 1

1 1 1 0 1 1 1 1

1 1 0 1 1 1 0 0

0 0 0 1 0 0 0 0

0 0 1 0 0 0 1 1

Comments Forward Forward Right Left Forward Forward Right Right

Figure 3.7: Truth table for robot action.

#define right_turn_signal 6

//digital pin - right_turn_signal

#define left_motor #define right_motor

//motor outputs //digital pin - left_motor //digital pin - right_motor

11 10

int left_IR_sensor_value; variable for left IR sensor int center_IR_sensor_value; variable for center IR sensor int right_IR_sensor_value; variable for right IR sensor

//declare //declare //declare

void setup() { pinMode(wall_left, OUTPUT); pinMode(wall_center, OUTPUT); pinMode(wall_right, OUTPUT);

//LED indicators - wall detectors //configure pin 1 for digital output //configure pin 2 for digital output //configure pin 3 for digital output

//LED indicators - turn signals pinMode(left_turn_signal,OUTPUT); //configure pin 0 for digital output pinMode(right_turn_signal,OUTPUT); //configure pin 4 for digital output

pinMode(left_motor,

OUTPUT);

//motor outputs - PWM //configure pin 11 for digital output


pinMode(right_motor, OUTPUT); }

//configure pin 10 for digital output

void loop() { //read analog output from IR sensors left_IR_sensor_value = analogRead(left_IR_sensor); center_IR_sensor_value = analogRead(center_IR_sensor); right_IR_sensor_value = analogRead(right_IR_sensor); //robot action table row 0 if((left_IR_sensor_value < 512)&&(center_IR_sensor_value < 512)&& (right_IR_sensor_value < 512)) { //wall detection LEDs digitalWrite(wall_left, LOW); //turn LED off digitalWrite(wall_center, LOW); //turn LED off digitalWrite(wall_right, LOW); //turn LED off //motor control analogWrite(left_motor, 128); //0 (off) to 255 (full speed) analogWrite(right_motor, 128); //0 (off) to 255 (full speed) //turn signals digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off analogWrite(left_motor, 0); //turn motor off analogWrite(right_motor,0); //turn motor off }

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//robot action table row 1 else if((left_IR_sensor_value < 512)&&(center_IR_sensor_value < 512)&& (right_IR_sensor_value > 512)) { //wall detection LEDs digitalWrite(wall_left, LOW); //turn LED off digitalWrite(wall_center, LOW); //turn LED off digitalWrite(wall_right, HIGH); //turn LED on //motor control analogWrite(left_motor, 128); //0 (off) to 255 (full speed) analogWrite(right_motor, 128); //0 (off) to 255 (full speed) //turn signals digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off analogWrite(left_motor, 0); //turn motor off analogWrite(right_motor,0); //turn motor off } //robot action table row 2 else if((left_IR_sensor_value < 512)&&(center_IR_sensor_value > 512)&& (right_IR_sensor_value < 512)) { //wall detection LEDs digitalWrite(wall_left, LOW); //turn LED off digitalWrite(wall_center, HIGH); //turn LED on digitalWrite(wall_right, LOW); //turn LED off //motor control analogWrite(left_motor, 128);


//0 (off) to 255 (full speed) analogWrite(right_motor, 0); //0 (off) to 255 (full speed) digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, analogWrite(left_motor, 0); analogWrite(right_motor,0); }

LOW); HIGH); LOW); LOW); LOW); HIGH); LOW); LOW);

//turn signals //turn LED off //turn LED on //delay 500 ms //turn LED off //turn LED off //delay 500 ms //turn LED off //turn LED on //delay 500 ms //turn LED off //turn LED off //turn motor off //turn motor off

//robot action table row 3 else if((left_IR_sensor_value < 512)&&(center_IR_sensor_value > 512)&& (right_IR_sensor_value > 512)) { //wall detection LEDs digitalWrite(wall_left, LOW); //turn LED off digitalWrite(wall_center, HIGH); //turn LED on digitalWrite(wall_right, HIGH); //turn LED on //motor control analogWrite(left_motor, 0); //0 (off) to 255 (full speed) analogWrite(right_motor, 128); //0 (off) to 255 (full speed) //turn signals digitalWrite(left_turn_signal, HIGH); //turn LED on digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms

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digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, analogWrite(left_motor, 0); analogWrite(right_motor,0); }

HIGH); LOW); LOW); LOW);

//turn LED on //turn LED off //delay 500 ms //turn LED off //turn LED off //turn motor off //turn motor off

//robot action table row 4 else if((left_IR_sensor_value > 512)&&(center_IR_sensor_value < 512)&& (right_IR_sensor_value < 512)) { //wall detection LEDs digitalWrite(wall_left, HIGH); //turn LED on digitalWrite(wall_center, LOW); //turn LED off digitalWrite(wall_right, LOW); //turn LED off //motor control analogWrite(left_motor, 128); //0 (off) to 255 (full speed) analogWrite(right_motor, 128); //0 (off) to 255 (full speed) //turn signals digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off analogWrite(left_motor, 0); //turn motor off analogWrite(right_motor,0); //turn motor off } //robot action table row 5


else if((left_IR_sensor_value > 512)&&(center_IR_sensor_value < 512)&& (right_IR_sensor_value > 512)) { //wall detection LEDs digitalWrite(wall_left, HIGH); //turn LED on digitalWrite(wall_center, LOW); //turn LED off digitalWrite(wall_right, HIGH); //turn LED on //motor control analogWrite(left_motor, 128); //0 (off) to 255 (full speed) analogWrite(right_motor, 128); //0 (off) to 255 (full speed) //turn signals digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off analogWrite(left_motor, 0); //turn motor off analogWrite(right_motor,0); //turn motor off } //robot action table row 6 else if((left_IR_sensor_value > 512)&&(center_IR_sensor_value > 512)&& (right_IR_sensor_value < 512)) { //wall detection LEDs digitalWrite(wall_left, HIGH); //turn LED on digitalWrite(wall_center, HIGH); //turn LED on digitalWrite(wall_right, LOW); //turn LED off //motor control analogWrite(left_motor, 128); //0 (off) to 255 (full speed)

71

72


analogWrite(right_motor, 0); //0 (off) to 255 (full speed) digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, analogWrite(left_motor, 0); analogWrite(right_motor,0); }

LOW); HIGH); LOW); LOW); LOW); HIGH); LOW); LOW);

//turn signals //turn LED off //turn LED on //delay 500 ms //turn LED off //turn LED off //delay 500 ms //turn LED off //turn LED off //delay 500 ms //turn LED OFF //turn LED OFF //turn motor off //turn motor off

//robot action table row 7 else if((left_IR_sensor_value > 512)&&(center_IR_sensor_value > 512)&& (right_IR_sensor_value > 512)) { //wall detection LEDs digitalWrite(wall_left, HIGH); //turn LED on digitalWrite(wall_center, HIGH); //turn LED on digitalWrite(wall_right, HIGH); //turn LED on //motor control analogWrite(left_motor, 128); //0 (off) to 255 (full speed) analogWrite(right_motor, 0); //0 (off) to 255 (full speed) //turn signals digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, HIGH); //turn LED on delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off digitalWrite(right_turn_signal, LOW); //turn LED off delay(500); //delay 500 ms digitalWrite(left_turn_signal, LOW); //turn LED off

3.5. SUMMARY

digitalWrite(right_turn_signal, HIGH); delay(500); digitalWrite(left_turn_signal, LOW); digitalWrite(right_turn_signal, LOW); analogWrite(left_motor, 0); analogWrite(right_motor,0); }

73

//turn LED on //delay 500 ms //turn LED off //turn LED off //turn motor off //turn motor off

} //************************************************************************* Testing the control algorithm: It is recommended that the algorithm be first tested without the entire robot platform. This may be accomplished by connecting the three IR sensors and LEDS to the appropriate pins on the Arduino UNO R3 as specified in Figure 3.4. In place of the two motors and their interface circuits, two LEDs with the required interface circuitry may be used. The LEDs will illuminate to indicate the motors would be on during different test scenarios. Once this algorithm is fully tested in this fashion, the Arduino UNO R3 may be mounted to the robot platform and connected to the motors. Full up testing in the maze may commence. Enjoy!

3.5

SUMMARY

In this chapter, we discussed the design process, related tools, and applied the process to a real world design. As previously mentioned, this design example will be periodically revisited throughout the text. It is essential to follow a systematic, disciplined approach to embedded systems design to successfully develop a prototype that meets established requirements.

3.6

REFERENCES

• M. Anderson, Help Wanted: Embedded Engineers Why the United States is losing its edge in embedded systems, IEEE-USA Today’s Engineer, Feb 2008. • Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025 • M. Fowler with K. Scott “UML Distilled - A Brief Guide to the Standard Object Modeling Language,” 2nd edition. Boston:Addison-Wesley, 2000. • N. Dale and S.C. Lilly “Pascal Plus Data Structures,” 4th edition. Englewood Cliffs, NJ: Jones and Bartlett, 1995.

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3.7

CHAPTER PROBLEMS

1. What is an embedded system? 2. What aspects must be considered in the design of an embedded system? 3. What is the purpose of the structure chart, UML activity diagram, and circuit diagram? 4. Why is a system design only as good as the test plan that supports it? 5. During the testing process, when an error is found and corrected, what should now be accomplished? 6. Discuss the top-down design, bottom-up implementation concept. 7. Describe the value of accurate documentation. 8. What is required to fully document an embedded systems design? 9. Update the robot action truth table if the robot was equipped with four IR sensors.

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CHAPTER

4

Serial Communication Subsystem Objectives: After reading this chapter, the reader should be able to • Describe the differences between serial and parallel communication. • Provide definitions for key serial communications terminology. • Describe the operation of the Universal Synchronous and Asynchronous Serial Receiver and Transmitter (USART). • Program the USART for basic transmission and reception using the built-in features of the Arduino Development Environment. • Program the USART for basic transmission and reception using C. • Describe the operation of the Serial Peripheral Interface (SPI). • Program the SPI system using the built-in features of the Arduino Development Environment. • Program the SPI system using C. • Describe the purpose of the Two Wire Interface (TWI). • Program the Arduino UNO R3 processing board using ISP programming techniques.

4.1

OVERVIEW

Serial communication techniques provide a vital link between the Arduino UNO R3 processing board an certain input devices, output devices, and other microcontrollers. In this chapter, we investigate the serial communication features beginning with a review of serial communication concepts and terminology. We then investigate in turn the following serial communication systems available on the Arduino UNO R3 processing board: the Universal Synchronous and Asynchronous Serial Receiver and Transmitter (USART), the Serial Peripheral Interface (SPI) and the Two Wire Interface (TWI). We provide guidance on how to program the USART and SPI using built-in Arduino Development Environment features and the C programming language. We conclude the chapter with examples on how to connect an SD card to the Arduino UNO R3 and also how to program using In System Programming (ISP) techniques.

76

4. SERIAL COMMUNICATION SUBSYSTEM

4.2

SERIAL COMMUNICATIONS

Microcontrollers must often exchange data with other microcontrollers or peripheral devices. Data may be exchanged by using parallel or serial techniques. With parallel techniques, an entire byte of data is typically sent simultaneously from the transmitting device to the receiver device. While this is efficient from a time point of view, it requires eight separate lines for the data transfer. In serial transmission, a byte of data is sent a single bit at a time. Once eight bits have been received at the receiver, the data byte is reconstructed. While this is inefficient from a time point of view, it only requires a line (or two) to transmit the data. The ATmega328 is equipped with a host of different serial communication subsystems including the serial USART, the serial peripheral interface or SPI, and the Two-wire Serial Interface (TWI). What all of these systems have in common is the serial transmission of data. Before discussing the different serial communication features aboard the ATmega328, we review serial communication terminology.

4.3

SERIAL COMMUNICATION TERMINOLOGY

In this section, we review common terminology associated with serial communication. Asynchronous versus Synchronous Serial Transmission: In serial communications, the transmitting and receiving device must be synchronized to one another and use a common data rate and protocol. Synchronization allows both the transmitter and receiver to be expecting data transmission/reception at the same time.There are two basic methods of maintaining “sync” between the transmitter and receiver: asynchronous and synchronous. In an asynchronous serial communication system, such as the USART aboard the ATmega328, framing bits are used at the beginning and end of a data byte. These framing bits alert the receiver that an incoming data byte has arrived and also signals the completion of the data byte reception.The data rate for an asynchronous serial system is typically much slower than the synchronous system, but it only requires a single wire between the transmitter and receiver. A synchronous serial communication system maintains “sync” between the transmitter and receiver by employing a common clock between the two devices. Data bits are sent and received on the edge of the clock. This allows data transfer rates higher than with asynchronous techniques but requires two lines, data and clock, to connect the receiver and transmitter. Baud rate: Data transmission rates are typically specified as a Baud or bits per second rate. For example, 9600 Baud indicates the data is being transferred at 9600 bits per second. Full Duplex: Often serial communication systems must both transmit and receive data. To do both transmission and reception, simultaneously, requires separate hardware for transmission and reception. A single duplex system has a single complement of hardware that must be switched from transmission to reception configuration. A full duplex serial communication system has separate hardware for transmission and reception.

4.4. SERIAL USART

77

Non-return to Zero (NRZ) Coding Format: There are many different coding standards used within serial communications. The important point is the transmitter and receiver must use a common coding standard so data may be interpreted correctly at the receiving end. The Atmel ATmega328 uses a non-return to zero (NRZ) coding standard. In NRZ coding a logic one is signaled by a logic high during the entire time slot allocated for a single bit; whereas, a logic zero is signaled by a logic low during the entire time slot allocated for a single bit. The RS-232 Communication Protocol: When serial transmission occurs over a long distance additional techniques may be used to insure data integrity. Over long distances logic levels degrade and may be corrupted by noise. At the receiving end, it is difficult to discern a logic high from a logic low. The RS-232 standard has been around for some time. With the RS-232 standard (EIA-232), a logic one is represented with a -12 VDC level while a logic zero is represented by a +12 VDC level. Chips are commonly available (e.g., MAX232) that convert the 5 and 0 V output levels from a transmitter to RS-232 compatible levels and convert back to 5V and 0 V levels at the receiver. The RS-232 standard also specifies other features for this communication protocol. Parity: To further enhance data integrity during transmission, parity techniques may be used. Parity is an additional bit (or bits) that may be transmitted with the data byte. The ATmega328 uses a single parity bit. With a single parity bit, a single bit error may be detected. Parity may be even or odd. In even parity, the parity bit is set to one or zero such that the number of ones in the data byte including the parity bit is even. In odd parity, the parity bit is set to one or zero such that the number of ones in the data byte including the parity bit is odd. At the receiver, the number of bits within a data byte including the parity bit are counted to insure that parity has not changed, indicating an error, during transmission. ASCII: The American Standard Code for Information Interchange or ASCII is a standardized, seven bit method of encoding alphanumeric data. It has been in use for many decades, so some of the characters and actions listed in the ASCII table are not in common use today. However, ASCII is still the most common method of encoding alphanumeric data. The ASCII code is provided in Figure 4.1. For example, the capital letter “G” is encoded in ASCII as 0x47. The “0x” symbol indicates the hexadecimal number representation. Unicode is the international counterpart of ASCII. It provides standardized 16-bit encoding format for the written languages of the world. ASCII is a subset of Unicode. The interested reader is referred to the Unicode home page website, www.unicode.org, for additional information on this standardized encoding format.

4.4

SERIAL USART

The serial USART (or Universal Synchronous and Asynchronous Serial Receiver and Transmitter) provide for full duplex (two way) communication between a receiver and transmitter. This is accomplished by equipping the ATmega328 with independent hardware for the transmitter and receiver. The USART is typically used for asynchronous communication. That is, there is not a common clock between the transmitter and receiver to keep them synchronized with one another. To maintain synchronization between the transmitter and receiver, framing start and stop bits are used at

78


Least significant digit

Most significant digit

0x_0 0x_1 0x_2 0x_3 0x_4 0x_5 0x_6 0x_7 0x_8 0x_9 0x_A 0x_B 0x_C 0x_D 0x_E 0x_F

0x0_

0x1_

0x2_

0x3_

0x4_

0x5_

0x6_

0x7_

NUL SOH STX ETX EOT ENQ ACK BEL BS HT LF VT FF CR SO SI

DLE DC1 DC2 DC3 DC4 NAK SYN ETB CAN EM SUB ESC FS GS RS US

SP ! “ # $ % & ‘ ( ) * + ‘ . /

0 1 2 3 4 5 6 7 8 9 : ; < = > ?

@ A B C D E F G H I J K L M N O

P Q R S T U V W X Y Z [ \ ] ^ _

` a b c d e f g h i j k l m n o

p q r s t u v w x y z { | } ~ DEL

Figure 4.1: ASCII Code.The ASCII code is used to encode alphanumeric characters.The “0x” indicates hexadecimal notation in the C programming language.

the beginning and end of each data byte in a transmission sequence. The Atmel USART also has synchronous features. Space does not permit a discussion of these USART enhancements. The ATmega328 USART is quite flexible. It has the capability to be set to a variety of data transmission or Baud (bits per second) rates. The USART may also be set for data bit widths of 5 to 9 bits with one or two stop bits. Furthermore, the ATmega328 is equipped with a hardware generated parity bit (even or odd) and parity check hardware at the receiver. A single parity bit allows for the detection of a single bit error within a byte of data. The USART may also be configured to operate in a synchronous mode. We now discuss the operation, programming, and application of the USART. Due to space limitations, we cover only the most basic capability of this flexible and powerful serial communication system.

4.4.1

SYSTEM OVERVIEW

The block diagram for the USART is provided in Figure 4.2. The block diagram may appear a bit overwhelming but realize there are four basic pieces to the diagram: the clock generator, the transmission hardware, the receiver hardware, and three control registers (UCSRA, UCSBR, and UCSRC). We discuss each in turn.

4.4. SERIAL USART

79

Figure 4.2: Atmel AVR ATmega328 USART block diagram. (Figure used with permission of Atmel, Incorporated.)

80


4.4.1.1 USART Clock Generator

The USART Clock Generator provides the clock source for the USART system and sets the Baud rate for the USART. The Baud Rate is derived from the overall microcontroller clock source. The overall system clock is divided by the USART Baud rate Registers UBRR[H:L] and several additional dividers to set the Baud rate. For the asynchronous normal mode (U2X bit = 0), the Baud Rate is determined using the following expression: Baud rate = (system clock f requency)/(16(U BRR + 1)) where UBRR is the contents of the UBRRH and UBRRL registers (0 to 4095). Solving for UBRR yields: U BRR = ((system clock generator)/(16 × Baud rate)) − 1 4.4.1.2 USART Transmitter

The USART transmitter consists of a Transmit Shift Register. The data to be transmitted is loaded into the Transmit Shift Register via the USART I/O Data Register (UDR). The start and stop framing bits are automatically appended to the data within the Transmit Shift Register. The parity is automatically calculated and appended to the Transmit Shift Register. Data is then shifted out of the Transmit Shift Register via the TxD pin a single bit at a time at the established Baud rate. The USART transmitter is equipped with two status flags: the UDRE and the TXC. The USART Data Register Empty (UDRE) flag sets when the transmit buffer is empty indicating it is ready to receive new data. This bit should be written to a zero when writing the USART Control and Status Register A (UCSRA). The UDRE bit is cleared by writing to the USART I/O Data Register (UDR). The Transmit Complete (TXC) Flag bit is set to logic one when the entire frame in the Transmit Shift Register has been shifted out and there are no new data currently present in the transmit buffer. The TXC bit may be reset by writing a logic one to it. 4.4.1.3 USART Receiver The USART Receiver is virtually identical to the USART Transmitter except for the direction of the data flow is reversed. Data is received a single bit at a time via the RxD pin at the established Baud Rate. The USART Receiver is equipped with the Receive Complete (RXC) Flag. The RXC flag is logic one when unread data exists in the receive buffer. 4.4.1.4 USART Registers

In this section, we discuss the register settings for controlling the USART system. We have already discussed the function of the USART I/O Data Register (UDR) and the USART Baud Rate Registers (UBRRH and UBRRL). Note: The USART Control and Status Register C (UCSRC) and the USART Baud Rate Register High (UBRRH) are assigned to the same I/O location in the memory map. The URSEL bit (bit 7 of both registers) determine which register is being accessed.

4.4. SERIAL USART

81

The URSEL bit must be one when writing to the UCSRC register and zero when writing to the UBRRH register.

USART Control and Status Register A (UCSRA) RXC TXC UDRE FE DOR PE 7 USART Control and Status Register B (UCSRB)

U2X

MPCM 0

RXCIE TXCIE UDRIE RXEN TXEN UCSZ2 RXB8 TXB8 7

0

USART Control and Status Register C (UCSRC) URSEL=1

UMSEL UPM1 UPM0 USBS UCSZ1 UCSZ0 UCPOL

7

0

USART Data Register - UDR UDR(Read) RXB7

RXB6

RXB5

RXB4

RXB3

RXB2

RXB1

RXB0

UDR(Write) TXB7 TXB6

TXB5

TXB4

TXB3

TXB2

TXB1

TXB0

7

0

USART Baud Rate Registers - UBRRH and UBRRL UBRRH URSEL=0

---

---

---

UBRR11 UBRR10 UBRR9 UBRR8

UBRRL UBRR7 UBRR6 UBRR5 UBRR4 UBRR3 UBRR2 UBRR1 UBRR0

7

0

Figure 4.3: USART Registers.

USART Control and Status Register A (UCSRA) The UCSRA register contains the RXC, TXC, and the UDRE bits. The function of these bits have already been discussed. USART Control and Status Register B (UCSRB) The UCSRB register contains the Receiver Enable (RXEN) bit and the Transmitter Enable (TXEN) bit. These bits are the “on/off ” switch for the receiver and transmitter, respectively. The UCSRB register also contains the UCSZ2 bit.

82


The UCSZ2 bit in the UCSRB register and the UCSZ[1:0] bits contained in the UCSRC register together set the data character size. USART Control and Status Register C (UCSRC) The UCSRC register allows the user to customize the data features to the application at hand. It should be emphasized that both the transmitter and receiver be configured with the same data features for proper data transmission.The UCSRC contains the following bits: • USART Mode Select (UMSEL) – 0: asynchronous operation, 1: synchronous operation • USART Parity Mode (UPM[1:0])- 00: no parity, 10: even parity, 11: odd parity • USART Stop Bit Select (USBS) – 0: 1 stop bit, 1: 2 stop bits • USART Character Size (data width) (UCSZ[2:0]) – 000: 5-bit, 001: 6-bit, 010: 7-bit, 011: 8-bit, 111: 9-bit

4.5

SYSTEM OPERATION AND PROGRAMMING USING ARDUINO DEVELOPMENT ENVIRONMENT FEATURES

The Arduino Development Environment is equipped with built-in USART communications features. These allow USART transmission (TX) and reception (RX) via Arduino UNO R3 DIGITAL pins 1 (TX) and 0 (RX) to an external USART compatible input device, output device, or microcontroller. The Arduino UNO R3 may also communicate with the host personal computer (PC) via the USB cable. The Arduino UNO R3 pins are configured for TTL compatible inputs and outputs. That is, logic highs and lows are represented with 5 VDC and 0 VDC signals, respectively. The TX and RX pins are not compatible with RS-232 signals. A level shifter such as the MAX232 is required between the Arduino UNO R3 and the RS-232 device for communications of this type. When connected to a PC via the USB cable, appropriate level shifting is accomplished via the USB support chip onboard the Arduino UNO R3. The Arduino Development Environment commands to provide USART communications is provided in Figure 4.4. A brief description of each command is provided. As before, we will not duplicate the excellent source material and examples provided at the Arduino homepage (www.Arduino.cc). Example: To illustrate the use of the Arduino Development Environment built-in serial functions using the USART, we will add code to the robot sketch to provide status updates to the host PC. These status updates are a helpful aid during algorithm development. Due to limited space, we will not provide the entire algorithm here (it is five pages long). Instead, we provide a code snapshot that may be used to modify the remaining code. In the code snapshot, we have included the “Serial.begin(9600)” command in the setup function to set the USART Baud rate at 9600. We have also inserted a “ Serial.println” command in the

4.5. SYSTEM OPERATION AND PROGRAMMING

83

Arduino Development Environment built-in USART commands [www.Arduino.cc] Command

Description

Serial.begin()

Sets Baud rate

Serial.end()

Disables serial communication. Allows Digital 1(TX) and Digital (0) RX to be used for digital input and output.

Serial.available()

Determines how many bytes have already been received and stored in the 128 byte buffer.

Serial.read()

Reads incoming serial data.

Serial.flush()

Flushes the serial receive buffer of data.

Serial.print()

Prints data to the serial port as ASCII text. An optional second parameter specifies the format for printing (BYTE, BIN, OCT, DEC, HEX).

Serial.println()

Prints data to the serial port as ASCII text followed by a carriage return.

Serial.write()

Writes binary data to the serial port. A single byte, a series of bytes, or an array of bytes may be sent.

Figure 4.4: Arduino Development Environment USART commands.

algorithm to provide a status update. These status updates are handy during sketch development. These status updates would not be available while the robot is progressing through the maze since the robot would no longer be connected to the host PC via the USB cable. //************************************************************************* //analog input pins #define left_IR_sensor 0 //analog pin - left IR sensor #define center_IR_sensor 1 #define right_IR_sensor 2

//analog pin - center IR sensor //analog pin - right IR sensor

#define wall_left #define wall_center #define wall_right

//digital output pins //LED indicators - wall detectors //digital pin - wall_left //digital pin - wall_center //digital pin - wall_right

3 4 5

84


#define left_turn_signal 2 #define right_turn_signal 6

//LED indicators - turn signals //digital pin - left_turn_signal //digital pin - right_turn_signal

#define left_motor #define right_motor


11 10

int left_IR_sensor_value; int center_IR_sensor_value; int right_IR_sensor_value; void setup() { Serial.begin(9600); pinMode(wall_left, OUTPUT); pinMode(wall_center, OUTPUT); pinMode(wall_right, OUTPUT);

//declare var. for left IR sensor //declare var. for center IR sensor //declare var. for right IR sensor

//set USART Baud rate to 9600 //LED indicators - wall detectors //configure pin 1 for digital output //configure pin 2 for digital output //configure pin 3 for digital output

//LED indicators - turn signals pinMode(left_turn_signal,OUTPUT); //configure pin 0 for digital output pinMode(right_turn_signal,OUTPUT); //configure pin 4 for digital output

pinMode(left_motor, OUTPUT); pinMode(right_motor, OUTPUT); }

//motor outputs - PWM //configure pin 11 for digital output //configure pin 10 for digital output

void loop() { //read analog output from IR sensors left_IR_sensor_value = analogRead(left_IR_sensor); center_IR_sensor_value = analogRead(center_IR_sensor); right_IR_sensor_value = analogRead(right_IR_sensor); //robot action table row 0 if((left_IR_sensor_value < 512)&&(center_IR_sensor_value < 512)&&

4.6. SYSTEM OPERATION AND PROGRAMMING IN C

85

(right_IR_sensor_value < 512)) { Serial.println(‘‘No walls detected’’); digitalWrite(wall_left, LOW); digitalWrite(wall_center, LOW); digitalWrite(wall_right, LOW); analogWrite(left_motor, //0 (off) to 255 (full analogWrite(right_motor, //0 (off) to 255 (full

//print status //wall detection LEDs //turn LED off //turn LED off //turn LED off //motor control

128); speed) 128); speed)

digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, delay(500); digitalWrite(left_turn_signal, digitalWrite(right_turn_signal, analogWrite(left_motor, 0); analogWrite(right_motor,0); }

LOW); LOW); LOW); LOW); LOW); LOW); LOW); LOW);

//turn signals //turn LED off //turn LED off //delay 500 ms //turn LED off //turn LED off //delay 500 ms //turn LED off //turn LED off //delay 500 ms //turn LED off //turn LED off //turn motor off //turn motor off

: :

4.6

SYSTEM OPERATION AND PROGRAMMING IN C

The basic activities of the USART system consist of initialization, transmission, and reception.These activities are summarized in Figure 4.5. Both the transmitter and receiver must be initialized with the same communication parameters for proper data transmission. The transmission and reception activities are similar except for the direction of data flow. In transmission, we monitor for the UDRE flag to set indicating the data register is empty. We then load the data for transmission into the

86


UDR register. For reception, we monitor for the RXC bit to set indicating there is unread data in the UDR register. We then retrieve the data from the UDR register.

Has UDRE flag set?

Set USART communication parameters (data bits, stop bit, parity)

yes Load UDR register with data byte for transmission

Turn on transmitter and/or receiver

a) USART transmission

Set USART for asynchronous mode

no

no

Has RXC flag set? yes

Retrieve received data from UDR register

c) USART reception Set Baud Rate

b) USART initialization

Figure 4.5: USART Activities.

To program the USART, we implement the flow diagrams provided in Figure 4.5. In the sample code provided, we assume the ATmega328 is operating at 10 MHz, and we desire a Baud Rate of 9600, asynchronous operation, no parity, one stop bit, and eight data bits. To achieve 9600 Baud with an operating frequency of 10 MHz requires that we set the UBRR registers to 64 which is 0x40. //************************************************************************* //USART_init: initializes the USART system //************************************************************************* void USART_init(void) { UCSRA = 0x00; UCSRB = 0x08; UCSRC = 0x86; UBRRH = 0x00; UBRRL = 0x40;

//control register initialization //enable transmitter //async, no parity, 1 stop bit, 8 data bits //Baud Rate initialization


87

} //************************************************************************* //USART_transmit: transmits single byte of data //************************************************************************* void USART_transmit(unsigned char data) { while((UCSRA & 0x20)==0x00) //wait for UDRE flag { ; } UDR = data; //load data to UDR for transmission } //************************************************************************* //USART_receive: receives single byte of data //************************************************************************* unsigned char USART_receive(void) { while((UCSRA & 0x80)==0x00) //wait for RXC flag { ; } data = UDR; //retrieve data from UDR return data; } //*************************************************************************

4.6.1

SERIAL PERIPHERAL INTERFACE—SPI

The ATmega328 Serial Peripheral Interface or SPI also provides for two-way serial communication between a transmitter and a receiver. In the SPI system, the transmitter and receiver share a common clock source. This requires an additional clock line between the transmitter and receiver but allows for higher data transmission rates as compared to the USART. The SPI system allows for fast and efficient data exchange between microcontrollers or peripheral devices. There are many SPI compatible external systems available to extend the features of the microcontroller. For example, a

88


liquid crystal display or a digital-to-analog converter could be added to the microcontroller using the SPI system. 4.6.1.1 SPI Operation

The SPI may be viewed as a synchronous 16-bit shift register with an 8-bit half residing in the transmitter and the other 8-bit half residing in the receiver as shown in Figure 4.6. The transmitter is designated the master since it is providing the synchronizing clock source between the transmitter and the receiver. The receiver is designated as the slave. A slave is chosen for reception by taking its Slave Select (SS) line low. When the SS line is taken low, the slave’s shifting capability is enabled. SPI transmission is initiated by loading a data byte into the master configured SPI Data Register (SPDR). At that time, the SPI clock generator provides clock pulses to the master and also to the slave via the SCK pin. A single bit is shifted out of the master designated shift register on the Master Out Slave In (MOSI) microcontroller pin on every SCK pulse. The data is received at the MOSI pin of the slave designated device. At the same time, a single bit is shifted out of the Master In Slave Out (MISO) pin of the slave device and into the MISO pin of the master device. After eight master SCK clock pulses, a byte of data has been exchanged between the master and slave designated SPI devices. Completion of data transmission in the master and data reception in the slave is signaled by the SPI Interrupt Flag (SPIF) in both devices. The SPIF flag is located in the SPI Status Register (SPSR) of each device. At that time, another data byte may be transmitted.

Master Device

Slave Device

SPI Data Register (SDR) MSB

MISO (PB6)

SCK SCK (PB7)

SCK (PB7)

SS (PB4)

SS (PB4)

SPI Status Register (SPSR) SPI Control Register (SPCR)

Figure 4.6: SPI Overview.

LSB

MOSI (PB5)

SCK SPI Clock Generator

SPI Data Register (SDR) MSB

LSB

MOSI (PB5) system clock

MISO (PB6)

shift enable


89

4.6.1.2 Registers

The registers for the SPI system are provided in Figure 4.7. We will discuss each one in turn. SPI Control Register - SPCR SPIE SPE DORD MSTR 7 SPI Status Register - SPSR SPIF

WCOL

---

7

---

CPOL CPHA

---

---

SPR1

SPR0 0

---

SPI2X 0

SPI Data Register - SPDR MSB

LSB

7

0

Figure 4.7: SPI Registers

SPI Control Register (SPCR) The SPI Control Register (SPCR) contains the “on/off ” switch for the SPI system. It also provides the flexibility for the SPI to be connected to a wide variety of devices with different data formats. It is important that both the SPI master and slave devices be configured for compatible data formats for proper data transmission. The SPCR contains the following bits: • SPI Enable (SPE) is the “on/off ” switch for the SPI system. A logic one turns the system on and logic zero turns it off. • Data Order (DORD) allows the direction of shift from master to slave to be controlled. When the DORD bit is set to one, the least significant bit (LSB) of the SPI Data Register (SPDR) is transmitted first. When the DORD bit is set to zero the Most Significant Bit (MSB) of the SPDR is transmitted first. • The Master/Slave Select (MSTR) bit determines if the SPI system will serve as a master (logic one) or slave (logic zero). • The Clock Polarity (CPOL) bit allows determines the idle condition of the SCK pin. When CPOL is one, SCK will idle logic high; whereas, when CPOL is zero, SCK will idle logic zero. • The Clock Phase (CPHA) determines if the data bit will be sampled on the leading (0) or trailing (1) edge of the SCK.

90


• The SPI SCK is derived from the microcontroller’s system clock source. The system clock is divided down to form the SPI SCK. The SPI Clock Rate Select bits SPR[1:0] and the Double SPI Speed Bit (SPI2X) are used to set the division factor. The following divisions may be selected using SPI2X, SPR1, SPR0: – 000: SCK = system clock/4 – 001: SCK = system clock/16 – 010: SCK = system clock/64 – 011: SCK = system clock/128 – 100: SCK = system clock/2 – 101: SCK = system clock/8 – 110: SCK = system clock/32 – 111: SCK = system clock/64 SPI Status Register (SPSR) The SPSR contains the SPI Interrupt Flag (SPIF). The flag sets when eight data bits have been transferred from the master to the slave. The SPIF bit is cleared by first reading the SPSR after the SPIF flag has been set and then reading the SPI Data Register (SPDR). The SPSR also contains the SPI2X bit used to set the SCK frequency. SPI Data Register (SPDR) SPI transmission.

4.7

As previously mentioned, writing a data byte to the SPDR initiates

SPI PROGRAMMING IN THE ARDUINO DEVELOPMENT ENVIRONMENT

The Arduino Development Environment provides the “shiftOut” command to provide ISP style serial communications [www.Arduino.cc]. The shiftOut command requires four parameters when called: • dataPin: the Arduino UNO R3 DIGITAL pin to be used for serial output. • clockPin: the Arduino UNO R3 DIGITAL pin to be used for the clock. • bitOrder: indicates whether the data byte will be sent most significant bit first (MSBFIRST) or least significant bit first (LSBFIRST). • value: the data byte that will be shifted out. To use the shiftOut command, the appropriate pins are declared as output using the pinMode command in the setup() function. The shiftOut command is then called at the appropriate place within the loop() function using the following syntax:

4.8. SPI PROGRAMMING IN C

91

shiftOut(dataPin, clockPin, LSBFIRST, value); As a result of the this command, the value specified will be serially shifted out of the data pin specified, least significant bit first, at the clock rate provided at the clock pin.

4.8

SPI PROGRAMMING IN C

To program the SPI system in C, the system must first be initialized with the desired data format. Data transmission may then commence. Functions for initialization, transmission and reception are provided below. In this specific example, we divide the clock oscillator frequency by 128 to set the SCK clock frequency. //************************************************************************* //spi_init: initializes spi system //************************************************************************* void spi_init(unsigned char control) { DDRB = 0xA0; //Set SCK (PB7), MOSI (PB5) for output, //others to input SPCR = 0x53; //Configure SPI Control Register (SPCR) //SPIE:0,SPE:1,DORD:0,MSTR:1,CPOL:0,CPHA:0,SPR:1,SPR0:1 } //************************************************************************* //spi_write: Used by SPI master to transmit a data byte //************************************************************************* void spi_write(unsigned char byte) { SPDR = byte; while (!(SPSR & 0x80)); } //************************************************************************* //spi_read: Used by SPI slave to receive data byte //************************************************************************* unsigned char spi_read(void) { while (!(SPSR & 0x80));

92


return SPDR; } //*************************************************************************

4.9

TWO-WIRE SERIAL INTERFACE—TWI

The TWI subsystem allows the system designer to network a number of related devices (microcontrollers, transducers, displays, memory storage, etc.) together into a system using a two wire interconnecting scheme. The TWI allows a maximum of 128 devices to be connected together. Each device has its own unique address and may both transmit and receive over the two wire bus at frequencies up to 400 kHz. This allows the device to freely exchange information with other devices in the network within a small area. Space does not permit a detailed discussion of this advanced serial communication system.

4.10 APPLICATION 1: SD/MMC CARD MODULE EXTENSION VIA THE USART The Secure Digital/Multi Media Card (SD/MMC) provides a “hard drive” capability to the Arduino UNO R3. That is, it provides a large capacity storage media to log and retrieve data. SD/MMC cards have become a common method of storing data in commercial industry. The card is formatted using the File Allocation Table (FAT) 16 standard. This standard has been around for some time. In this example, we show how to connect a Comfile Technology SD/MMC SD-COM5 card to the Arduino Microcontroller and the associated Arduino Development Environment commands required to interact with the card [www.comfiletech.com]. The commands will be passed to the SD/MMC card via the serial USART functions of the Arduino Development Environment. We also provide the commands for communicating with the SD/MMC via the C programming language. The interface circuit between the Arduino UNO R3 and the SD/MMC card is provided in Figure 4.8. The TX and RX pins (DIGITAL 1 and 0) of the Arduino UNO R3 are connected to the RXD and TXD pins (19 and 20) of the SD/MMC card breakout board. Power and ground are also provided to the SD/MMC card as shown in the figure. Also, the reset pin of the SD/MMC breakout board (pin 15) is pulled up to the 5 VDC supply via a 10K resistor. Figure 4.9 provides a summary of commands to communicate with the SD/MMC card. The command format is shown at the top of the figure. The commands are issued from the Arduino UNO R3 using the built-in “serial.print” command of the Arduino Development Environment. For example, to send the phrase “Hello World” to the SD/MMC the fputs command is used. The format of the command includes the file onboard the SD/MMC where the command should be stored and the file option. In this example we have used the “w” option to indicate a write to the file. The phrase for storage is then provided followed by a carriage return (\r) and a line feed (\n).

4.10. APPLICATION 1: SD/MMC CARD MODULE EXTENSION VIA THE USART

93

COMFILE SD-COM5 SD/MMC card module 1

20

TXD RXD GND SDIN VCC RST

SOUT SIN GND DNLD

10

5 VDC 10K

11 SD Card

TX RX

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

Arduino UNO R3

5VGnd

ANALOG IN 0 123 4 5

Figure 4.8: Arduino UNO R3 and SD/MMC card interface circuit [Comfile Technology].

Before data can be written to the file, some preparatory steps are required: • Set the Baud rate for communication. • Set the SD/MMC for MCU (microcontroller) mode.This mode provides simplified responses back to the Arduino UNO R3. • Initialize the SD/MMC card. • Create a file. Commands are provided for each of these actions in Figure 4.9. We will provide a complete sketch to communicate with the SD/MMC in the Applications section of the next chapter. Once data has been written to an SD/MMC card, it may be removed from the card socket in the breakout board and read via a PC using a universal card reader. Universal card readers are readily available for under $20. This would make the SD/MMC useful for a remote data logging

94

4. SERIAL COMMUNICATION SUBSYSTEM Command format: Command [Filename] [Option] [Data] [CR] [LF] In C: printf(fputs test.txt /w Hello World \r\n);

In Arduino Development Environment: serial.print(fputs test.txt /w Hello World \r\n);

Command

Brief Description

mode[Option][CR][LF]

Select mode of operation: /t terminal or /m MCU mode

init [CR][LF]

Initializes SD/MMC card

cd [Change Directory][CR][LF]

Change director

dir [CR][LF]

List directory

fsize [Filename][CR][LF]

Display file size

dsize[CR][LF]

Display SD/MMC disk space

ftime [Filename][CR][LF]

File creation and last modified time

md[Directory][CR][LF]

Make directory

rd[Directory][CR][LF]

Remove directory

del[Filename][CR][LF]

Delete file

fcreate[Filename][CR][LF]

Create a new file

rename[Source Filename][Destination Filename][CR][LF]

Rename the file

fopen[Filename][/Option][CR][LF]

Open the file: /r Read or /w Write or /a Append

fclose[CR][LF]

Close file

fputc[Filename][/Option][1 Byte Data][CR][LF]

Write a byte to file

fputs[Filename][/Option][String][CR][LF]

Write a string to file (limited 256 characters)

fwrite[/# of bytes to write][CR][LF]

Write up to 512 bytes to file

fgetc[/# of bytes to read][CR][LF]

Read up to 256 bytes from file

fgets[CR][LF]

Read one line of string

fread[Filename][CR][LF]

Read all data in file

reset[CR][LF]

Reset card

baud[Baud rate][CR][LF]

Set Baud rate

card[CR][LF]

Card status

Figure 4.9: SD/MMC commands.

4.11. APPLICATION 2: PROGRAMMING THE ARDUINO UNO R3 ATMEGA328 VIA ISP

95

application. Once the data has been collected, the card may be accessed via the PC, the data pulled into a spreadsheet application such as MS Office Excel and analyzed.

4.11 APPLICATION 2: PROGRAMMING THE ARDUINO UNO R3 ATMEGA328 VIA THE ISP An alternate method of programming the Arduino UNO R3 processing board is via In-System Programming (ISP) techniques. We highly recommend that you use the Arduino Development Environment for programming the Arduino UNO R3. The ISP programming techniques are used to program features of the ATmega328P hosted onboard the Arduino UNO R3 that are not currently supported within the Arduino Development Environment. Programming the ATmega328 requires several hardware and software tools. We briefly mention required components here. Please refer to the manufacturer’s documentation for additional details at www.atmel.com. Software Tools: Throughout the text, we use the ImageCraft ICC AVR compiler. This is a broadly used, user-friendly compiler. There are other excellent compilers available. The compiler is used to translate the source file (filename.c) into machine language for loading into the ATmega328 hosted onboard the Arduino UNO R3. We use Atmel’s AVR Studio to load the machine code into the ATmega328. Hardware Tools: We use Atmel’s STK500 AVR Flash MCU Starter Kit (STK500) for programming the ATmega328. The STK500 provides the interface hardware between the host PC and the ATmega328 for machine code loading. The STK500 is equipped with a complement of DIP sockets which allows for programming all of the microcontrollers in the Atmel AVR line. The STK500 also allows for In-System Programming (ISP) [Atmel]. In this example, we use the ISP programming features of the STK500.

4.11.1 PROGRAMMING PROCEDURE In this section, we provide a step-by-step procedure to program the ATmega328 hosted onboard the Arduino UNO R3 using the STK500 AVR Flash MCU Starter Kit. Please refer to Figure 4.10. 1. Load AVR Studio (free download from www.atmel.com). 2. Ensure that the STK500 is powered down. 3. Connect the STK500 as shown in Figure 4.10. Note: For ISP programming, the 6-wire ribbon cable is connected from the ISP6PIN header pin on the STK500 to the 6-pin header pin on the Arduino UNO R3, not the position of the red guide wire in the diagram. 4. Power up the STK500. 5. Start up AVR Studio on your PC.

96


indicates jumper block installed at this location red wire

VTARGET PORTA

Use this red socket

to power supply

ATMEL AVR

AREF

SWITCHES

RESET

RS232 cable to host PC

PORTB

XTAL1 ribbon cables

OSCSEL

PORTC red wire

RS232 CTRL

BSEL2 PORTD

SPROG3 PJUMP

RS232 SPARE

LEDS

PORTE

Note: red wire

3 21 0 9 8 76 5 4 32 1 0 1 11 1

ISP6PIN ISP10PIN

ribbon cable connecting STK500 ISP6PIN to Arduino Duemilanove 6-pin header

Note: red wire

Figure 4.10: Programming the ATmega328 onboard the Arduino UNO R3 with the STK500.

4.12. SUMMARY

97

6. Pop up window “Welcome to AVR Studio” should appear. Close this window by clicking on the “Cancel button.” 7. Click on the “AVR icon.” It looks like the silhouette of an integrated circuit. It is on the second line of the toolbar about half way across the screen. 8. This should bring up a STK500 pop up window with eight tabs (Main, Program, Fuses, Lockbits, Advanced, HW Settings, HW Info). At the bottom of the Main tab window, verify that the STK500 was autodetected. Troubleshoot as necessary to ensure STK500 was autodetected by AVR Studio. 9. Set all tab settings: • Main: – Device and Signature Bytes: ATmega328P – Programming Mode and Target Setting: ISP Mode – Depress “Read Signature” to insure the STK500 is communicating with the Arduino UNO R3 • Program: – Flash: Input HEX file, Browse and find machine code file: – EEPROM: Input HEX file, Browse and find machine code file: 10. Programming step: • Program Tab: click program 11. Power down the STK500. Disconnect the STK500 from the Arduino UNO R3 processing board.

4.12 SUMMARY In this chapter, we have discussed the differences between parallel and serial communications and key serial communication related terminology. We then in turn discussed the operation of USART, SPI and TWI serial communication systems. We also provided basic code examples to communicate with the USART and SPI systems.

4.13 REFERENCES • Atmel 8-bit AVR Microcontroller with 4/8/16/32K Bytes In-System Programmable Flash, ATmega48PA/88PA/168PA/328P data sheet: 8161D-AVR-10/09, Atmel Corporation, 2325 Orchard Parkway, San Jose, CA 95131.

98


• Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025 • Serial SD/MMC Card www.comfiletech.com.

Module

User

Manual,

Comfile

Technology,

Inc.,

4.14 CHAPTER PROBLEMS 1. Summarize the differences between parallel and serial conversion. 2. Summarize the differences between the USART, SPI, and TWI methods of serial communication. 3. Draw a block diagram of the USART system, label all key registers, and all keys USART flags. 4. Draw a block diagram of the SPI system, label all key registers, and all keys USART flags. 5. If an ATmega328 microcontroller is operating at 12 MHz what is the maximum transmission rate for the USART and the SPI? 6. What is the ASCII encoded value for “Arduino”? 7. Draw the schematic of a system consisting of two ATmega328s that will exchange data via the SPI system. 8. Write the code to implement the system described in the question above.

99

CHAPTER

5

Analog to Digital Conversion (ADC) Objectives: After reading this chapter, the reader should be able to • Illustrate the analog-to-digital conversion process. • Assess the quality of analog-to-digital conversion using the metrics of sampling rate, quantization levels, number of bits used for encoding and dynamic range. • Design signal conditioning circuits to interface sensors to analog-to-digital converters. • Implement signal conditioning circuits with operational amplifiers. • Describe the key registers used during an ATmega328 ADC. • Describe the steps to perform an ADC with the ATmega328. • Program the Arduino UNO R3 processing board to perform an ADC using the built-in features of the Arduino Development Environment. • Program the ATmega328 to perform an ADC in C. • Describe the operation of a digital-to-analog converter (DAC).

5.1

OVERVIEW

A microcontroller is used to process information from the natural world, decide on a course of action based on the information collected, and then issue control signals to implement the decision. Since the information from the natural world, is analog or continuous in nature, and the microcontroller is a digital or discrete based processor, a method to convert an analog signal to a digital form is required. An ADC system performs this task while a digital to analog converter (DAC) performs the conversion in the opposite direction. We will discuss both types of converters in this chapter. Most microcontrollers are equipped with an ADC subsystem; whereas, DACs must be added as an external peripheral device to the controller. In this chapter, we discuss the ADC process in some detail. In the first section, we discuss the conversion process itself, followed by a presentation of the successive-approximation hardware implementation of the process. We then review the basic features of the ATmega328 ADC system

100

5. ANALOG TO DIGITAL CONVERSION (ADC)

followed by a system description and a discussion of key ADC registers.We conclude our discussion of the analog-to-digital converter with several illustrative code examples. We show how to program the ADC using the built-in features of the Arduino Development Environment and C. We conclude the chapter with a discussion of the DAC process and interface a multi-channel DAC to the ATmega328. We also discuss the Arduino Development Environment built-in features that allow generation of an output analog signal via pulse width modulation (PWM) techniques. Throughout the chapter, we provide detailed examples.

5.2

SAMPLING, QUANTIZATION AND ENCODING

In this subsection, we provide an abbreviated discussion of the ADC process. This discussion was condensed from “Atmel AVR Microcontroller Primer Programming and Interfacing.” The interested reader is referred to this text for additional details and examples [Barrett and Pack]. We present three important processes associated with the ADC: sampling, quantization, and encoding. Sampling. We first start with the subject of sampling. Sampling is the process of taking ‘snap shots’ of a signal over time. When we sample a signal, we want to sample it in an optimal fashion such that we can capture the essence of the signal while minimizing the use of resources. In essence, we want to minimize the number of samples while retaining the capability to faithfully reconstruct the original signal from the samples. Intuitively, the rate of change in a signal determines the number of samples required to faithfully reconstruct the signal, provided that all adjacent samples are captured with the same sample timing intervals. Sampling is important since when we want to represent an analog signal in a digital system, such as a computer, we must use the appropriate sampling rate to capture the analog signal for a faithful representation in digital systems. Harry Nyquist from Bell Laboratory studied the sampling process and derived a criterion that determines the minimum sampling rate for any continuous analog signals. His, now famous, minimum sampling rate is known as the Nyquist sampling rate, which states that one must sample a signal at least twice as fast as the highest frequency content of the signal of interest. For example, if we are dealing with the human voice signal that contains frequency components that span from about 20 Hz to 4 kHz, the Nyquist sample theorem requires that we must sample the signal at least at 8 kHz, 8000 ‘snap shots’ every second. Engineers who work for telephone companies must deal with such issues. For further study on the Nyquist sampling rate, refer to Pack and Barrett listed in the References section. When a signal is sampled a low pass anti-aliasing filter must be employed to insure the Nyquist sampling rate is not violated. In the example above, a low pass filter with a cutoff frequency of 4 KHz would be used before the sampling circuitry for this purpose. Quantization. Now that we understand the sampling process, let’s move on to the second process of the analog-to-digital conversion, quantization. Each digital system has a number of bits it uses as the basic unit to represent data. A bit is the most basic unit where single binary information, one or zero, is represented. A nibble is made up of four bits put together. A byte is eight bits.

5.2. SAMPLING, QUANTIZATION AND ENCODING

101

We have tacitly avoided the discussion of the form of captured signal samples. When a signal is sampled, digital systems need some means to represent the captured samples. The quantization of a sampled signal is how the signal is represented as one of the quantization levels. Suppose you have a single bit to represent an incoming signal. You only have two different numbers, 0 and 1. You may say that you can distinguish only low from high. Suppose you have two bits. You can represent four different levels, 00, 01, 10, and 11. What if you have three bits? You now can represent eight different levels: 000, 001, 010, 011, 100, 101, 110, and 111. Think of it as follows. When you had two bits, you were able to represent four different levels. If we add one more bit, that bit can be one or zero, making the total possibilities eight. Similar discussion can lead us to conclude that given n bits, we have 2n unique numbers or levels one can represent. Figure 5.1 shows how n bits are used to quantize a range of values. In many digital systems, the incoming signals are voltage signals. The voltage signals are first obtained from physical signals (pressure, temperature, etc.) with the help of transducers, such as microphones, angle sensors, and infrared sensors. The voltage signals are then conditioned to map their range with the input range of a digital system, typically 0 to 5 volts. In Figure 5.1, n bits allow you to divide the input signal range of a digital system into 2n different quantization levels. As can be seen from the figure, the more quantization levels means the better mapping of an incoming signal to its true value. If we only had a single bit, we can only represent level 0 and level 1. Any analog signal value in between the range had to be mapped either as level 0 or level 1, not many choices. Now imagine what happens as we increase the number of bits available for the quantization levels. What happens when the available number of bits is 8? How many different quantization levels are available now? Yes, 256. How about 10, 12, or 14? Notice also that as the number of bits used for the quantization levels increases for a given input range the ‘distance’ between two adjacent levels decreases accordingly. Finally, the encoding process involves converting a quantized signal into a digital binary number. Suppose again we are using eight bits to quantize a sampled analog signal. The quantization levels are determined by the eight bits and each sampled signal is quantized as one of 256 quantization levels. Consider the two sampled signals shown in Figure 5.1. The first sample is mapped to quantization level 2 and the second one is mapped to quantization level 198. Note the amount of quantization error introduced for both samples. The quantization error is inversely proportional to the number of bits used to quantize the signal. Encoding. Once a sampled signal is quantized, the encoding process involves representing the quantization level with the available bits. Thus, for the first sample, the encoded sampled value is 0000_0001, while the encoded sampled value for the second sample is 1100_0110. As a result of the encoding process, sampled analog signals are now represented as a set of binary numbers. Thus, the encoding is the last necessary step to represent a sampled analog signal into its corresponding digital form, shown in Figure 5.1.

102


Voltage reference high level n-1

sampled value 2

level 198 - encoded level 1100 0110

Analog Signal

sampled value 1

level 1 - encoded level 0000 0001 Voltage reference low

t(s)

Ts = 1/fs

sample time

Figure 5.1: Sampling, quantization, and encoding.

5.2.1

RESOLUTION AND DATA RATE

Resolution. Resolution is a measure used to quantize an analog signal. In fact, resolution is nothing more than the voltage ‘distance’ between two adjacent quantization levels we discussed earlier. Suppose again we have a range of 5 volts and one bit to represent an analog signal. The resolution in this case is 2.5 volts, a very poor resolution. You can imagine how your TV screen will look if you only had only two levels to represent each pixel, black and white. The maximum error, called the resolution error, is 2.5 volts for the current case, 50 % of the total range of the input signal. Suppose you now have four bits to represent quantization levels. The resolution now becomes 1.25 volts or 25 % of the input range. Suppose you have 20 bits for quantization levels. The resolution now becomes 4.77 × 10−6 volts, 9.54 × 10−5 % of the total range. The discussion we presented simply illustrates that as we increase the available number of quantization levels within a fixed voltage range, the distance between adjacent levels decreases, reducing the quantization error of a sampled signal. As the number grows, the error decreases, making the representation of a sampled analog signal more accurate in the corresponding digital form. The number of bits used for the quantization is directly proportional to the resolution of a system. You now should understand the technical background when you watch high definition television broadcasting. In general, resolution may be defined as: resolution = (voltage span)/2b = (Vref

high

− Vref

low )/2

b

5.3. ANALOG-TO-DIGITAL CONVERSION (ADC) PROCESS

103

for the ATmega328, the resolution is: resolution = (5 − 0)/210 = 4.88 mV Data rate. The definition of the data rate is the amount of data generated by a system per some time unit. Typically, the number of bits or the number of bytes per second is used as the data rate of a system. We just saw that the more bits we use for the quantization levels, the more accurate we can represent a sampled analog signal.Why not use the maximum number of bits current technologies can offer for all digital systems, when we convert analog signals to digital counterparts? It has to do with the cost involved. In particular, suppose you are working for a telephone company and your switching system must accommodate 100,000 customers. For each individual phone conversation, suppose the company uses an 8KHz sampling rate (fs ) and you are using 10 bits for the quantization levels for each sampled signal.1 This means the voice conversation will be sampled every 125 microseconds (Ts ) due to the reciprocal relationship between (fs ) and (Ts ). If all customers are making out of town calls, what is the number of bits your switching system must process to accommodate all calls? The answer will be 100,000 x 8000 x 10 or eight billion bits per every second! You will need some major computing power to meet the requirement for processing and storage of the data. For such reasons, when designers make decisions on the number of bits used for the quantization levels and the sampling rate, they must consider the computational burden the selection will produce on the computational capabilities of a digital system versus the required system resolution. Dynamic range. You will also encounter the term “dynamic range” when you consider finding appropriate analog-to-digital converters. The dynamic range is a measure used to describe the signal to noise ratio. The unit used for the measurement is Decibel (dB), which is the strength of a signal with respect to a reference signal. The greater the dB number, the stronger the signal is compared to a noise signal. The definition of the dynamic range is 20 log 2b where b is the number of bits used to convert analog signals to digital signals. Typically, you will find 8 to 12 bits used in commercial analog-to-digital converters, translating the dynamic range from 20 log 28 dB to 20 log 212 dB.

5.3

ANALOG-TO-DIGITAL CONVERSION (ADC) PROCESS

The goal of the ADC process is to accurately represent analog signals as digital signals. Toward this end, three signal processing procedures, sampling, quantization, and encoding, described in the previous section must be combined together. Before the ADC process takes place, we first need to convert a physical signal into an electrical signal with the help of a transducer. A transducer is an electrical and/or mechanical system that converts physical signals into electrical signals or electrical signals to physical signals. Depending on the purpose, we categorize a transducer as an input transducer or an output transducer. If the conversion is from physical to electrical, we call it an input transducer. The mouse, the keyboard, and the microphone for your personal computer all fall under this category. A camera, an infrared sensor, and a temperature sensor are also input transducers. 1 For the sake of our discussion, we ignore other overheads involved in processing a phone call such as multiplexing, de-multiplexing,

and serial-to-parallel conversion.

104


The output transducer converts electrical signals to physical signals. The computer screen and the printer for your computer are output transducers. Speakers and electrical motors are also output transducers. Therefore, transducers play the central part for digital systems to operate in our physical world by transforming physical signals to and from electrical signals. It is important to carefully design the interface between transducers and the microcontroller to insure proper operation. A poorly designed interface could result in improper embedded system operation or failure. Interface techniques are discussed in detail in Chapter 8.

5.3.1

TRANSDUCER INTERFACE DESIGN (TID) CIRCUIT

In addition to transducers, we also need a signal conditioning circuitry before we apply the ADC. The signal conditioning circuitry is called the transducer interface. The objective of the transducer interface circuit is to scale and shift the electrical signal range to map the output of the input transducer to the input range of the analog-to-digital converter which is typically 0 to 5 VDC. Figure 5.2 shows the transducer interface circuit using an input transducer.

Xmax

V1max V1min

Xmin Input Transducer

V2max

K

V2min

Scalar Multiplier

B

ADC Input

(Bias)

Figure 5.2: A block diagram of the signal conditioning for an analog-to-digital converter. The range of the sensor voltage output is mapped to the analog-to-digital converter input voltage range. The scalar multiplier maps the magnitudes of the two ranges and the bias voltage is used to align two limits.

The output of the input transducer is first scaled by constant K. In the figure, we use a microphone as the input transducer whose output ranges from -5 VDC to + 5 VDC. The input to the analog-to-digital converter ranges from 0 VDC to 5 VDC. The box with constant K maps the output range of the input transducer to the input range of the converter. Naturally, we need to multiply all input signals by 1/2 to accommodate the mapping. Once the range has been mapped, the signal now needs to be shifted. Note that the scale factor maps the output range of the input transducer as -2.5 VDC to +2.5 VDC instead of 0 VDC to 5 VDC. The second portion of the circuit shifts the range by 2.5 VDC, thereby completing the correct mapping. Actual implementation of the TID circuit components is accomplished using operational amplifiers. In general, the scaling and bias process may be described by two equations:


105

V2max = (V1max × K) + B V2min = (V1min × K) + B The variable V1max represents the maximum output voltage from the input transducer. This voltage occurs when the maximum physical variable (Xmax ) is presented to the input transducer. This voltage must be scaled by the scalar multiplier (K) and then have a DC offset bias voltage (B) added to provide the voltage V2max to the input of the ADC converter [USAFA]. Similarly, The variable V1min represents the minimum output voltage from the input transducer. This voltage occurs when the minimum physical variable (Xmin ) is presented to the input transducer. This voltage must be scaled by the scalar multiplier (K) and then have a DC offset bias voltage (B) added to produce voltage V2min to the input of the ADC converter. Usually, the values of V1max and V1min are provided with the documentation for the transducer. Also, the values of V2max and V2min are known. They are the high and low reference voltages for the ADC system (usually 5 VDC and 0 VDC for a microcontroller). We thus have two equations and two unknowns to solve for K and B. The circuits to scale by K and add the offset B are usually implemented with operational amplifiers. Example: A photodiode is a semiconductor device that provides an output current corresponding to the light impinging on its active surface. The photodiode is used with a transimpedance amplifier to convert the output current to an output voltage. A photodiode/transimpedance amplifier provides an output voltage of 0 volts for maximum rated light intensity and -2.50 VDC output voltage for the minimum rated light intensity. Calculate the required values of K and B for this light transducer so it may be interfaced to a microcontroller’s ADC system. V2max = (V1max × K) + B V2min = (V1min × K) + B 5.0 V = (0 V × K) + B 0 V = (−2.50 V × K) + B The values of K and B may then be determined to be 2 and 5 VDC, respectively.

5.3.2

OPERATIONAL AMPLIFIERS

In the previous section, we discussed the transducer interface design (TID) process. Going through this design process yields a required value of gain (K) and DC bias (B). Operational amplifiers (op amps) are typically used to implement a TID interface. In this section, we briefly introduce

106


operational amplifiers including ideal op amp characteristics, classic op amp circuit configurations, and an example to illustrate how to implement a TID with op amps. Op amps are also used in a wide variety of other applications including analog computing, analog filter design, and a myriad of other applications. We do not have the space to investigate all of these related applications. The interested reader is referred to the References section at the end of the chapter for pointers to some excellent texts on this topic. 5.3.2.1 The ideal operational amplifier

A generic ideal operational amplifier is illustrated in Figure 5.3. An ideal operational does not exist in the real world. However, it is a good first approximation for use in developing op amp application circuits. Vcc Vn

Vp

In Ip

Vo

-

Vcc

saturation

Vo = Avol (Vp - Vn)

+

linear region -Vcc Ideal conditions: -- In = Ip = 0 -- Vp = Vn -- Avol >> 50,000 -- Vo = Avol (Vp - Vn)

Vi = Vp - Vn

saturation

-Vcc

Figure 5.3: Ideal operational amplifier characteristics.

The op amp is an active device (requires power supplies) equipped with two inputs, a single output, and several voltage source inputs. The two inputs are labeled Vp, or the non-inverting input, and Vn, the inverting input. The output of the op amp is determined by taking the difference between Vp and Vn and multiplying the difference by the open loop gain (Avol ) of the op amp which is typically a large value much greater than 50,000. Due to the large value of Avol , it does not take much of a difference between Vp and Vn before the op amp will saturate. When an op amp saturates, it does not damage the op amp, but the output is limited to the supply voltages ±Vcc . This will clip the output, and hence distort the signal, at levels slightly less than ±Vcc . Op amps are typically used in a closed loop, negative feedback configuration. A sample of classic operational amplifier configurations with negative feedback are provided in Figure 5.4 [Faulkenberry]. It should be emphasized that the equations provided with each operational amplifier circuit are only valid if the circuit configurations are identical to those shown. Even a slight variation in the circuit configuration may have a dramatic effect on circuit operation. It is important to analyze each operational amplifier circuit using the following steps:


Rf +Vcc

-

+Vcc

Ri

-

Vin

+

Vout = Vin

+

Vout = - (Rf / Ri)(Vin)

Vin

-Vcc

-Vcc

a) Inverting amplifier

b) Voltage follower

Rf V1

+Vcc

Ri

+Vcc

-

Vout = ((Rf + Ri)/Ri)(Vin)

+ Vin

V2

-Vcc

-Vcc

Ri

V3

R2 R3

Rf d) Differential input amplifier

Rf

R1

Vout = (Rf/Ri)(V2 -V1)

+

c) Non-inverting amplifier

V1 V2

Rf

Ri

Rf +Vcc

+Vcc

+ -Vcc

Vout = - (Rf / R1)(V1) - (Rf / R2)(V2) - (Rf / R3)(V3)

-

-Vcc

f) Transimpedance amplifier (current-to-voltage converter)

e) Scaling adder amplifier

Rf C Vin

Vout = - (I Rf)

+

I

C +Vcc

+Vcc

Rf

-

Vout = - Rf C (dVin/dt)

+ -Vcc

g) Differentiator

Vin

Vout = - 1/(Rf C) (Vindt)

+ -Vcc

h) Integrator

Figure 5.4: Classic operational amplifier configurations. Adapted from [Faulkenberry].

107

108


• Write the node equation at Vn for the circuit. • Apply ideal op amp characteristics to the node equation. • Solve the node equation for Vo. As an example, we provide the analysis of the non-inverting amplifier circuit in Figure 5.5. This same analysis technique may be applied to all of the circuits in Figure 5.4 to arrive at the equations for Vout provided.

Node equation at Vn:

Rf

(Vn - Vin)/ Ri + (Vn - Vout)/Rf + In = 0 Vn

Ri In Vin

Ip

+Vcc

Apply ideal conditions:

Vout

+ Vp

In = Ip = 0 Vn = Vp = 0 (since Vp is grounded)

-Vcc

Solve node equation for Vout: Vout = - (Rf / Ri)(Vin)

Figure 5.5: Operational amplifier analysis for the non-inverting amplifier. Adapted from [Faulkenberry].

Example: In the previous section, it was determined that the values of K and B were 2 and 5 VDC, respectively. The two-stage op amp circuitry provided in Figure 5.6 implements these values of K and B. The first stage provides an amplification of -2 due to the use of the non-inverting amplifier configuration. In the second stage, a summing amplifier is used to add the output of the first stage with a bias of – 5 VDC. Since this stage also introduces a minus sign to the result, the overall result of a gain of 2 and a bias of +5 VDC is achieved.

5.4

ADC CONVERSION TECHNOLOGIES

The ATmega328 uses a successive-approximation converter technique to convert an analog sample into a 10-bit digital representation. In this section, we will discuss this type of conversion process. For a review of other converter techniques, the interested reader is referred to “Atmel AVR Microcontroller Primer: Programming and Interfacing.” In certain applications, you are required to use converter technologies external to the microcontroller.

5.5. THE ATMEL ATMEGA328 ADC SYSTEM

109

Rf = 20K Rf = 10K +Vcc

Ri = 10K Vin

+Vcc

-

Ri = 10K

+

-

-Vcc

Ri = 10K

-Vcc

10K

bias = 5 VDC

Vout

+ -Vcc

Figure 5.6: Operational amplifier implementation of the transducer interface design (TID) example circuit.

5.4.1

SUCCESSIVE-APPROXIMATION

The ATmega328 microcontroller is equipped with a successive-approximation ADC converter. The successive-approximation technique uses a digital-to-analog converter, a controller, and a comparator to perform the ADC process. Starting from the most significant bit down to the least significant bit, the controller turns on each bit at a time and generates an analog signal, with the help of the digital-to-analog converter, to be compared with the original input analog signal. Based on the result of the comparison, the controller changes or leaves the current bit and turns on the next most significant bit. The process continues until decisions are made for all available bits. Figure 5.7 shows the architecture of this type of converter. The advantage of this technique is that the conversion time is uniform for any input, but the disadvantage of the technology is the use of complex hardware for implementation.

5.5

THE ATMEL ATMEGA328 ADC SYSTEM

The Atmel ATmega328 microcontroller is equipped with a flexible and powerful ADC system. It has the following features [Atmel]: • 10-bit resolution • ±2 least significant bit (LSB) absolute accuracy • 13 ADC clock cycle conversion time • 6 multiplexed single ended input channels

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Analog input signal Analog reference signal

Digital-to-analog converter

Controller

Start Conversion

Comparator

Serial digital output

Successive-approximation converter

Figure 5.7: Successive-approximation ADC.

• Selectable right or left result justification • 0 to Vcc ADC input voltage range Let’s discuss each feature in turn. The first feature of discussion is “10-bit resolution.” Resolution is defined as: Resolution = (VRH − VRL )/2b VRH and VRL are the ADC high and low reference voltages. Whereas, “b” is the number of bits available for conversion. For the ATmega328 with reference voltages of 5 VDC, 0 VDC, and 10-bits available for conversion, resolution is 4.88 mV. Absolute accuracy specified as ±2 LSB is then ±9.76 mV at this resolution [Atmel]. It requires 13 analog-to-digital clock cycles to perform an ADC conversion.The ADC system may be run at a slower clock frequency than the main microcontroller clock source. The main microcontroller clock is divided down using the ADC Prescaler Select (ADPS[2:0]) bits in the ADC Control and Status Register A (ADCSRA). A slower ADC clock results in improved ADC accuracy at higher controller clock speeds. The ADC is equipped with a single successive-approximation converter. Only a single ADC channel may be converted at a given time. The input of the ADC is equipped with an six input


111

analog multiplexer. The analog input for conversion is selected using the MUX[3:0] bits in the ADC Multiplexer Selection Register (ADMUX). The 10-bit result from the conversion process is placed in the ADC Data Registers, ADCH and ADCL. These two registers provide 16 bits for the 10-bit result. The result may be left justified by setting the ADLAR (ADC Left Adjust Result) bit of the ADMUX register. Right justification is provided by clearing this bit. The analog input voltage for conversion must be between 0 and Vcc volts. If this is not the case, external circuitry must be used to insure the analog input voltage is within these prescribed bounds as discussed earlier in the chapter.

5.5.1

BLOCK DIAGRAM

The block diagram for the ATmega328 ADC conversion system is provided in Figure 5.8. The left edge of the diagram provides the external microcontroller pins to gain access to the ADC. The six analog input channels are provided at ADC[5:0] and the ADC reference voltage pins are provided at AREF and AVCC. The key features and registers of the ADC system previously discussed are included in the diagram.

5.5.2

REGISTERS

The key registers for the ADC system are shown in Figure 5.9. It must be emphasized that the ADC system has many advanced capabilities that we do not discuss here. Our goal is to review the basic ADC conversion features of this powerful system. We have already discussed many of the register setting already. We will discuss each register in turn [Atmel]. 5.5.2.1 ADC Multiplexer Selection Register (ADMUX)

As previously discussed, the ADMUX register contains the ADLAR bit to select left or right justification and the MUX[3:0] bits to determine which analog input will be provided to the analogto-digital converter for conversion. To select a specific input for conversion is accomplished when a binary equivalent value is loaded into the MUX[3:0] bits. For example, to convert channel ADC7, “0111” is loaded into the ADMUX register. This may be accomplished using the following C instruction: ADMUX = 0x07; The REFS[1:0] bits of the ADMUX register are also used to determine the reference voltage source for the ADC system. These bits may be set to the following values: • REFS[0:0] = 00: AREF used for ADC voltage reference • REFS[0:1] = 01: AVCC with external capacitor at the AREF pin • REFS[1:0] = 10: Reserved

112


Figure 5.8: Atmel AVR ATmega328 ADC block diagram. (Figure used with permission of Atmel, Incorporated.)


113

ADC Multiplexer Selection Register - ADMUX REFS1 REFS0 ADLAR --- MUX3 MUX2 MUX1 MUX0 7 0 ADC Control and Status Register A - ADCSRA ADEN ADSC ADATE ADIF 7

ADIE ADPS2 ADPS1 ADPS0 0

ADC Data Register - ADCH and ADCL (ADLAR = 0) --15 ADC7

---

---

---

---

---

ADC6 ADC5 ADC4 ADC3 ADC2

ADC9 ADC8 ADCH ADC1

7

8 ADC0 ADCL 0

ADC Data Register - ADCH and ADCL (ADLAR = 1) ADC9 ADC8 ADC7 15 ADC1

ADC6 ADC5 ADC4 ADC3 ADC2 ADCH 8

ADC0

---

---

7

---

---

---

---

ADCL

0

Figure 5.9: ADC Registers. Adapted from Atmel.

• REFS[1:1] = 11: Internal 1.1 VDC voltage reference with an external capacitor at the AREF pin 5.5.2.2 ADC Control and Status Register A (ADCSRA) The ADCSRA register contains the ADC Enable (ADEN) bit. This bit is the “on/off ” switch for the ADC system. The ADC is turned on by setting this bit to a logic one. The ADC Start Conversion (ADSC) bit is also contained in the ADCSRA register. Setting this bit to logic one initiates an ADC. The ADCSRA register also contains the ADC Interrupt flag (ADIF) bit. This bit sets to logic one when the ADC is complete. The ADIF bit is reset by writing a logic one to this bit. The ADC Prescaler Select (ADPS[2:0]) bits are used to set the ADC clock frequency. The ADC clock is derived from dividing down the main microcontroller clock. The ADPS[2:0] may be set to the following values:

• ADPS[2:0] = 000: division factor 2

114


• ADPS[2:0] = 001: division factor 2 • ADPS[2:0] = 010: division factor 4 • ADPS[2:0] = 011: division factor 8 • ADPS[2:0] = 100: division factor 16 • ADPS[2:0] = 101: division factor 32 • ADPS[2:0] = 110: division factor 64 • ADPS[2:0] = 111: division factor 128 5.5.2.3 ADC Data Registers (ADCH, ADCL)

As previously discussed, the ADC Data Register contains the result of the ADC. The results may be left (ADLAR=1) or right (ADLAR=0) justified.

5.6

PROGRAMMING THE ADC USING THE ARDUINO DEVELOPMENT ENVIRONMENT

The Arduino Development Environment has the built-in function analogRead to perform an ADC conversion. The format for the analogRead function is: unsigned int return_value;

return_value = analogRead(analog_pin_read); The function returns an unsigned integer value from 0 to 1023, corresponding to the voltage span from 0 to 5 VDC. Recall that we introduced the use of this function in the Application section at the end of Chapter 3. The analogRead function was used to read the analog output values from the three IR sensors on the Blinky 602A robot.

5.7

PROGRAMMING THE ADC IN C

Provided below are two functions to operate the ATmega328 ADC system. The first function “InitADC( )” initializes the ADC by first performing a dummy conversion on channel 0. In this particular example, the ADC prescalar is set to 8 (the main microcontroller clock was operating at 10 MHz). The function then enters a while loop waiting for the ADIF bit to set indicating the conversion is complete. After conversion the ADIF bit is reset by writing a logic one to it. The second function, “ReadADC(unsigned char),” is used to read the analog voltage from the specified ADC channel. The desired channel for conversion is passed in as an unsigned character

5.7. PROGRAMMING THE ADC IN C

115

variable. The result is returned as a left justified, 10 bit binary result. The ADC prescalar must be set to 8 to slow down the ADC clock at higher external clock frequencies (10 MHz) to obtain accurate results. After the ADC is complete, the results in the eight bit ADCL and ADCH result registers are concatenated into a 16-bit unsigned integer variable and returned to the function call. //************************************************************************* //InitADC: initialize analog-to-digital converter //************************************************************************* void InitADC( void) { ADMUX = 0; ADCSRA = 0xC3;

//Select channel 0 //Enable ADC & start 1st dummy //conversion //Set ADC module prescalar to 8

while (!(ADCSRA & 0x10)); ADCSRA |= 0x10; }

//critical for accurate ADC results //Check if conversation is ready //Clear conv rdy flag - set the bit

//************************************************************************* //ReadADC: read analog voltage from analog-to-digital converter //the desired channel for conversion is passed in as an unsigned //character variable. //The result is returned as a right justified, 10 bit binary result. //The ADC prescalar must be set to 8 to slow down the ADC clock at higher //external clock frequencies (10 MHz) to obtain accurate results. //*************************************************************************

unsigned int ReadADC(unsigned char channel) { unsigned int binary_weighted_voltage, binary_weighted_voltage_low; //weighted binary voltage unsigned int binary_weighted_voltage_high; ADMUX = channel; ADCSRA |= 0x43;

//Select channel //Start conversion

116


//Set ADC module prescalar to 8 //critical for accurate ADC results while (!(ADCSRA & 0x10)); //Check if conversion is ready ADCSRA |= 0x10; //Clear Conv rdy flag - set the bit binary_weighted_voltage_low = ADCL; //Read 8 low bits first (important) //Read 2 high bits, multiply by 256 binary_weighted_voltage_high = ((unsigned int)(ADCH << 8)); binary_weighted_voltage = binary_weighted_voltage_low | binary_weighted_voltage_high; return binary_weighted_voltage; //ADCH:ADCL } //*************************************************************************

5.8

EXAMPLE: ADC RAIN GAGE INDICATOR

In this example, we construct a rain gage type level display using small light emitting diodes. The rain gage indicator consists of a panel of eight light emitting diodes. The gage may be constructed from individual diodes or from an LED bar containing eight elements. Whichever style is chosen, the interface requirements between the processor and the LEDs are the same. The requirement for this project is to use the analog-to-digital converter to illuminate up to eight LEDs based on the input voltage. A 10k trimmer potentiometer is connected to the ADC channel to vary the input voltage. We first provide a solution using the Arduino Development Environment with the Arduino UNO R3 processing board. Then a solution employing the ATmega328 programmed in C is provided.

5.8.1

ADC RAIN GAGE INDICATOR USING THE ARDUINO DEVELOPMENT ENVIRONMENT

The circuit configuration employing the Arduino UNO R3 processing board is provided in Figure 5.10. The DIGITAL pins of the microcontroller are used to communicate with the LED interface circuit. We describe the operation of the LED interface circuit in Chapter 8. The sketch to implement the project requirements is provided below. As in previous examples, we define the Arduino UNO R3 pins, set them for output via the setup() function, and write the loop() function. In this example, the loop() function senses the voltage from the 10K trimmer potentiometer and illuminates a series of LEDs corresponding to the sensed voltage levels. //************************************************************************* #define trim_pot 0 //analog input pin //digital output pins //LED indicators 0 - 7

5.8. EXAMPLE: ADC RAIN GAGE INDICATOR

Vcc = 5 V 220

2N2222

Vcc = 5 V 220

10K

2N2222 10K

Vcc = 5 V 220

2N2222

Vcc = 5 V 220

10K

2N2222 10K

Vcc = 5 V 220

2N2222

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

Vcc = 5 V 220

10K

2N2222 10K

Arduino UNO R3

Vcc = 5 V 220

2N2222

5VGnd

Vcc = 5 V 220

10K ANALOG IN 0 123 4 5

2N2222 10K

Vcc = 5 V 10K

Figure 5.10: ADC with rain gage level indicator.

117

118


#define #define #define #define #define #define #define #define

LED0 LED1 LED2 LED3 LED4 LED5 LED6 LED7

0 1 2 3 4 5 6 7

int trim_pot_reading;

//digital //digital //digital //digital //digital //digital //digital //digital

pin pin pin pin pin pin pin pin

//declare variable for trim pot

void setup() { pinMode(LED0, pinMode(LED1, pinMode(LED2, pinMode(LED3, pinMode(LED4, pinMode(LED5, pinMode(LED6, pinMode(LED7, }

OUTPUT); OUTPUT); OUTPUT); OUTPUT); OUTPUT); OUTPUT); OUTPUT); OUTPUT);

//LED indicators - wall detectors //configure pin 0 for digital output //configure pin 1 for digital output //configure pin 2 for digital output //configure pin 3 for digital output //configure pin 4 for digital output //configure pin 5 for digital output //configure pin 6 for digital output //configure pin 7 for digital output

void loop() { //read analog output from trim pot trim_pot_reading = analogRead(trim_pot); if(trim_pot_reading < 128) { digitalWrite(LED0, HIGH); digitalWrite(LED1, LOW); digitalWrite(LED2, LOW); digitalWrite(LED3, LOW); digitalWrite(LED4, LOW); digitalWrite(LED5, LOW); digitalWrite(LED6, LOW);


digitalWrite(LED7, LOW); } else if(trim_pot_reading < 256) { digitalWrite(LED0, HIGH); digitalWrite(LED1, HIGH); digitalWrite(LED2, LOW); digitalWrite(LED3, LOW); digitalWrite(LED4, LOW); digitalWrite(LED5, LOW); digitalWrite(LED6, LOW); digitalWrite(LED7, LOW); } else if(trim_pot_reading < 384) { digitalWrite(LED0, HIGH); digitalWrite(LED1, HIGH); digitalWrite(LED2, HIGH); digitalWrite(LED3, LOW); digitalWrite(LED4, LOW); digitalWrite(LED5, LOW); digitalWrite(LED6, LOW); digitalWrite(LED7, LOW); } else if(trim_pot_reading < 512) { digitalWrite(LED0, HIGH); digitalWrite(LED1, HIGH); digitalWrite(LED2, HIGH); digitalWrite(LED3, HIGH); digitalWrite(LED4, LOW); digitalWrite(LED5, LOW); digitalWrite(LED6, LOW); digitalWrite(LED7, LOW); } else if(trim_pot_reading < 640) { digitalWrite(LED0, HIGH); digitalWrite(LED1, HIGH);

119

120


digitalWrite(LED2, HIGH); digitalWrite(LED3, HIGH); digitalWrite(LED4, HIGH); digitalWrite(LED5, LOW); digitalWrite(LED6, LOW); digitalWrite(LED7, LOW); } else if(trim_pot_reading < 768) { digitalWrite(LED0, HIGH); digitalWrite(LED1, HIGH); digitalWrite(LED2, HIGH); digitalWrite(LED3, HIGH); digitalWrite(LED4, HIGH); digitalWrite(LED5, HIGH); digitalWrite(LED6, LOW); digitalWrite(LED7, LOW); } else if(trim_pot_reading < 896) { digitalWrite(LED0, HIGH); digitalWrite(LED1, HIGH); digitalWrite(LED2, HIGH); digitalWrite(LED3, HIGH); digitalWrite(LED4, HIGH); digitalWrite(LED5, HIGH); digitalWrite(LED6, HIGH); digitalWrite(LED7, LOW); } else { digitalWrite(LED0, digitalWrite(LED1, digitalWrite(LED2, digitalWrite(LED3, digitalWrite(LED4, digitalWrite(LED5, digitalWrite(LED6,

HIGH); HIGH); HIGH); HIGH); HIGH); HIGH); HIGH);


121

digitalWrite(LED7, HIGH); } delay(500); }

//delay 500 ms

//*************************************************************************

5.8.2

ADC RAIN GAGE INDICATOR IN C

We now implement the rain gage indicator with the control algorithm (sketch) programmed in C for the ATmega328. The circuit configuration employing the ATmega328 is provided in Figure 5.11. PORT D of the microcontroller is used to communicate with the LED interface circuit. In this example, we extend the requirements of the project: • Write a function to display an incrementing binary count from 0 to 255 on the LEDs. • Write a function to display a decrementing binary count from 255 to 0 on the LEDs. • Use the analog-to-digital converter to illuminate up to eight LEDs based on the input voltage. A 10k trimmer potentiometer is connected to the ADC channel to vary the input voltage. The algorithm for the project was written by Anthony (Tony) Kunkel, MSEE and Geoff Luke, MSEE, at the University of Wyoming for an Industrial Controls class assignment. A 30 ms delay is provided between PORTD LED display updates. This prevents the display from looking as a series of LEDs that are always illuminated. Note: The delay function provided in this example is not very accurate. It is based on counting the number of assembly language no operation (NOPs). If a single NOP requires a single clock cycle to execute. A rough (and inaccurate) estimation of expended time may be calculated. The actual delay depends on the specific resolution of clock source used with the microcontroller, the clock frequency of the clock source and the specific compiler used to implement the code. In this specific example an accurate delay is not required since we are simply trying to slow down the code execution time so the LED changes may be observed. In the next chapter we provide a more accurate method of providing a time delay based on counting interrupts. //************************************************************************* //Tony Kunkel and Geoff Luke //University of Wyoming //************************************************************************* //This program calls four functions: //First: Display an incrementing binary count on PORTD from 0-255 //Second: Display a decrementing count on PORTD from 255-0 //Third: Display rain gauge info on PORTD

122


Vcc = 5 V 220

2N2222 10K

Vcc = 5 V 220

2N2222 10K

Atmega328

VDD

1M

sys reset 1.0 uF

1 PUR - PC6 2 RXD1 - PD0 3 TXD1 - PD1 4 PD2 5 PD3 6 PD4 7 Vcc 8 GND 9 PB6 10 PB7 11 PD5 12 PD6 13 PD7 14 PB0

PC5 28 PC4 27 PC3 26 PC2 25 PC1 24 PCO 23 GND 22 AREF 21 AVCC 20 PB5 19 PB4 18 PB3 17 PB2 16 PB1 15

Vcc = 5 V

Vcc = 5 V 220

10K 2N2222 VDD

10K

Vcc = 5 V 220

2N2222 10K

Vcc = 5 V 220

2N2222 10K

Vcc = 5 V 220

2N2222 10K

Vcc = 5 V 220

2N2222 10K

Vcc = 5 V 220

2N2222 10K

Figure 5.11: ADC with rain gage level indicator.


123

//Fourth: Delay when ever PORTD is updated //************************************************************************* //ATMEL register definitions for ATmega328 #include //function prototypes void display_increment(void); to display increment to PORTD void display_decrement(void); to display decrement to PORTD void rain_gage(void) void InitADC(void); unsigned int ReadADC(); void delay(void);

//Function //Function

//Initialize ADC converter //Read specified ADC channel //Function to delay

//************************************************************************* int main(void) { display_increment();

//Display incrementing binary on

delay();

//PORTD from 0-255 //Delay

display_decrement();

//Display decrementing binary on

delay();

//PORTD from 255-0 //Delay

InitADC(); while(1) { rain_gage(); delay(); } return 0;

//Display gage info on PORTD //Delay

124


}

//************************************************************************* //function definitions //************************************************************************* //************************************************************************* //delay //Note: The delay function provided in this example is not very accurate. //It is based on counting the number of assembly language no operation //(NOPs). If a single NOP requires a single clock cycle to execute. A //rough (and inaccurate) estimation of expended time may be calculated. //The actual delay depends on the specific resolution of clock source //used with the microcontroller, the clock frequency of the clock source //and the specific compiler used to implement the code. In this specific //example an accurate delay is not required since we are simply trying to //slow down the code execution time so the LED changes may be observed. //************************************************************************* void delay(void) { int i, k; for(i=0; i<400; i++) { for(k=0; k<300; k++) { asm("nop"); } } }

//assembly language nop, requires 2 cycles

//************************************************************************* //Displays incrementing binary count from 0 to 255 //************************************************************************* void display_increment(void)


125

{ int i; unsigned char j = 0x00; DDRD = 0xFF;

//set PORTD to output

for(i=0; i<255; i++) { j++; PORTD = j; delay(); } }

//increment j //assign j to data port //wait

//************************************************************************* //Displays decrementing binary count from 255 to 0 //************************************************************************* void display_decrement(void) { int i; unsigned char j = 0xFF; DDRD = 0xFF;


for(i=0; i<256; i++) { j=(j-0x01); PORTD = j; delay(); } }

//decrement j by one //assign char j to data port //wait

//************************************************************************* //Initializes ADC //************************************************************************* void InitADC(void)

126


{ ADMUX = 0; ADCSRA = 0xC3;

while (!(ADCSRA & 0x10)); ADCSRA |= 0x10; }

//Select channel 0 //Enable ADC & start dummy conversion //Set ADC module prescalar //to 8 critical for //accurate ADC results //Check if conversation is ready //Clear conv rdy flag - set the bit

//************************************************************************* //ReadADC: read analog voltage from analog-to-digital converter //the desired channel for conversion is passed in as an unsigned //character variable. The result is returned as a right justified, //10 bit binary result. //The ADC prescalar must be set to 8 to slow down the ADC clock at //higher external clock frequencies (10 MHz) to obtain accurate results. //************************************************************************* unsigned int ReadADC(unsigned char channel) { unsigned int binary_weighted_voltage, binary_weighted_voltage_low; unsigned int binary_weighted_voltage_high; //weighted binary voltage ADMUX = channel; ADCSRA |= 0x43;

//Select channel //Start conversion //Set ADC module prescalar //to 8 critical for //accurate ADC results while (!(ADCSRA & 0x10)); //Check if conversion is ready ADCSRA |= 0x10; //Clear Conv rdy flag - set the bit binary_weighted_voltage_low = ADCL; //Read 8 low bits first-(important) //Read 2 high bits, multiply by 256 binary_weighted_voltage_high = ((unsigned int)(ADCH << 8)); binary_weighted_voltage = binary_weighted_voltage_low | binary_weighted_voltage_high; return binary_weighted_voltage; //ADCH:ADCL }


127

//************************************************************************* //Displays voltage magnitude as LED level on PORTB //************************************************************************* void rain_gage(void) { unsigned int ADCValue; ADCValue = readADC(0x00); DDRD = 0xFF; if(ADCValue < 128) { PORTD = 0x01; } else if(ADCValue < { PORTD = 0x03; } else if(ADCValue < { PORTD = 0x07; } else if(ADCValue < { PORTD = 0x0F; } else if(ADCValue < { PORTD = 0x1F; } else if(ADCValue < { PORTD = 0x3F; } else if(ADCValue < { PORTD = 0x7F;


256)

384)

512)

640)

768)

896)

128


} else { PORTD = 0xAA; } } //************************************************************************* //*************************************************************************

5.8.3

ADC RAIN GAGE USING THE ARDUINO DEVELOPMENT ENVIRONMENT—REVISITED

If you carefully compare the two implementations of the rain gage indicator provided in the two previous examples, you will note that some activities are easier to perform in the Arduino Development Environment while others are easier to accomplish in C. Is it possible to mix the two techniques for a more efficient sketch? The answer is “yes!” In this example, we revise the earlier Arduino Development Environment sketch using portions of the original sketch with the ATmega328 control algorithm code to significantly shorten the program. In particular, we will address PORTD directly in the sketch to shorten up the code when the LEDs are illuminated. Recall in Chapter 1, we provided the open source schematic of the Arduino UNO R3 processing board (Figure 1.8). Careful study of the schematic reveals that DIGITAL pins 7 to 0 are connected to PORTD of the Arduino UNO R3 processing board. This allows direct configuration of PORTD using C language constructs. //************************************************************************* #define trim_pot 0 //analog input pin int trim_pot_reading;

//declare variable for trim pot

void setup() { DDRD = 0xFF; }

//Set PORTD (DIGITAL pins 7 to 0) //as output

void loop() { //read analog output from trim pot trim_pot_reading = analogRead(trim_pot); if(trim_pot_reading < 128) {

5.9. ONE-BIT ADC - THRESHOLD DETECTOR

PORTD = 0x01; } else if(trim_pot_reading < 256) { PORTD = 0x03; } else if(trim_pot_reading < 384) { PORTD = 0x07; } else if(trim_pot_reading < 512) { PORTD = 0x0F; } else if(trim_pot_reading < 640) { PORTD = 0x1F; } else if(trim_pot_reading < 768) { PORTD = 0x3F; } else if(trim_pot_reading < 896) { PORTD = 0x7F; } else { PORTD = 0xFF; } delay(500); }

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//illuminate LED 0

//illuminate LED 0-1






//illuminate LED 0-7 //delay 500 ms

//*************************************************************************

5.9

ONE-BIT ADC - THRESHOLD DETECTOR

A threshold detector circuit or comparator configuration contains an operational amplifier employed in the open loop configuration. That is, no feedback is provided from the output back to the input to limit gain. A threshold level is applied to one input of the op amp. This serves as a comparison

130


reference for the signal applied to the other input. The two inputs are constantly compared to one another. When the input signal is greater than the set threshold value, the op amp will saturate to a value slightly less than +Vcc as shown in Figure 5.12a). When the input signal falls below the threshold the op amp will saturate at a voltage slightly greater than –Vcc. If a single-sided op amp is used in the circuit (e.g., LM324), the –Vcc supply pin may be connected to ground. In this configuration, the op map provides for a one-bit ADC circuit. A bank of threshold detectors may be used to construct a multi-channel threshold detector as shown in Figure 5.12c). This provides a flash converter type ADC. It is a hardware version of a rain gage indicator. In Chapter 1, we provided a 14-channel version for use in a laboratory instrumentation project.

5.10 DIGITAL-TO-ANALOG CONVERSION (DAC) Once a signal is acquired to a digital system with the help of the analog-to digital conversion process and has been processed, frequently the processed signal is converted back to another analog signal. A simple example of such a conversion occurs in digital audio processing. Human voice is converted to a digital signal, modified, processed, and converted back to an analog signal for people to hear. The process to convert digital signals to analog signals is completed by a digital-to-analog converter. The most commonly used technique to convert digital signals to analog signals is the summation method shown in Figure 5.13. With the summation method of digital-to-analog conversion, a digital signal, represented by a set of ones and zeros, enters the digital-to-analog converter from the most significant bit to the least significant bit. For each bit, a comparator checks its logic state, high or low, to produce a clean digital bit, represented by a voltage level. Typically, in a microcontroller context, the voltage level is +5 or 0 volts to represent logic one or logic zero, respectively. The voltage is then multiplied by a scalar value based on its significant position of the digital signal as shown in Figure 5.13. Once all bits for the signal have been processed, the resulting voltage levels are summed together to produce the final analog voltage value. Notice that the production of a desired analog signal may involve further signal conditioning such as a low pass filter to ‘smooth’ the quantized analog signal and a transducer interface circuit to match the output of the digital-to-analog converter to the input of an output transducer.

5.10.1 DAC WITH THE ARDUINO DEVELOPMENT ENVIRONMENT The analogWrite command within the Arduino Development Environment issues a signal from 0 to 5 VDC by sending a constant from 0 to 255 using pulse width modulation (PWM) techniques. This signal, when properly filtered, serves as a DC signal. The Blinky 602A control sketch provided in Chapter 3 used the analogWrite command to issue drive signals to the robot motors to navigate the robot through the maze. The form of the analogWrite command is the following: analogWrite(output pin, value);

5.10. DIGITAL-TO-ANALOG CONVERSION (DAC)

Vo Vcc

+Vcc= 5 V Vp

Vi +Vcc

Vn

+

saturation

Vi > Vth

Vout

saturation

-

Vi Vth

Vth

b) Transfer characteristic for threshold detector

a) Threshold detector +5 VDC

voltage level for comparison

+5 VDC

10K

(4)

4/5 supply

+5 VDC

(2) (1) (3)

10K

(11)

220

small LED 3/5 supply

(6)

(7)

(5) 220

10K


(9) (8) (10)

10K

220


(13) (14) (12) 220

10K

small LED

threshold detectors c) 4-channel threshold detector

Figure 5.12: One-bit ADC threshold detector.

131

132


comparators MSB

scalar multipliers 1/2

1/4

1/8

LSB

quantized analog signal adder

1/2n

2.5 v

Figure 5.13: A summation method to convert a digital signal into a quantized analog signal. Comparators are used to clean up incoming signals and the resulting values are multiplied by a scalar multiplier and the results are added to generate the output signal. For the final analog signal, the quantized analog signal should be connected to a low pass filter followed by a transducer interface circuit.

5.10.2 DAC WITH EXTERNAL CONVERTERS A microcontroller can be equipped with a wide variety of DAC configurations including: • Single channel, 8-bit DAC connected via a parallel port (e.g., Motorola MC1408P8) • Quad channel, 8-bit DAC connected via a parallel port (e.g., Analog Devices AD7305) • Quad channel, 8-bit DAC connected via the SPI (e.g., Analog Devices AD7304) • Octal channel, 8-bit DAC connected via the SPI (e.g., Texas Instrument TLC5628) Space does not allow an in depth look at each configuration, but we will examine the TLC5628 in more detail.

5.11. APPLICATION: ART PIECE ILLUMINATION SYSTEM – REVISITED

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5.10.3 OCTAL CHANNEL, 8-BIT DAC VIA THE SPI The Texas Instruments (TI) TLC5628 is an eight channel, 8-bit DAC connected to the microcontroller via the SPI. Reference Figure 5.14a). It has a wide range of features packed into a 16-pin chip including [Texas Instrument]: • Eight individual, 8-bit DAC channels, • Operation from a single 5 VDC supply, • Data load via the SPI interface, • Programmable gain (1X or 2X), and • A 12-bit command word to program each DAC. Figure 5.14b) provides the interconnection between the ATmega328 and the TLC5628. The ATmega328 SPI’s SCK line is connected to the TLC5628: the MOSI to the serial data line and PORTB[2] to the Load line. As can be seen in the timing diagram, two sequential bytes are sent from the ATmega328 to select the appropriate DAC channel and to provide updated data to the DAC. The Load line is pulsed low to update the DAC. In this configuration, the LDAC line is tied low. The function to transmit data to the DAC is left as an assignment for the reader at the end of the chapter.

5.11 APPLICATION: ART PIECE ILLUMINATION SYSTEM – REVISITED In Chapter 2, we investigated an illumination system for a painting. The painting was to be illuminated via high intensity white LEDs. The LEDs could be mounted in front of or behind the painting as the artist desired. We equipped the lighting system with an IR sensor to detect the presence of someone viewing the piece. We also wanted to adjust the intensity of the lighting based on how the close viewer was to the art piece. A circuit diagram of the system is provided in Figure 5.15. The Arduino Development Environment sketch to sense how away the viewer is and issue a proportional intensity control signal to illuminate the LED is provided below. The analogRead function is used to obtain the signal from the IR sensor. The analogWrite function is used to issue a proportional signal. //************************************************************************* //analog input pins #define viewer_sensor 0 //analog pin - left IR sensor

#define illumination_output

0

//digital output pins //illumination output pin

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buffer REF1 latch

gain

DAC

latch

DACA

RNG

buffer

buffer

REF2 latch

A[2:0] CLK DATA LOAD LDAC

D[7:0]

gain

DAC

latch

RNG

DACE buffer

RNG

serial interface

a) TLC5628 octal 8-bit DACs ATmega164/TLC5628

MOSI/DATA

CLK LOW

CLK LOW

SCK/CLK

A2

A1

A0

RNG

D7

D6

D5

D4

D3

D2

PORTB[2]/Load

b) TLC5628 timing diagram

A[2:0] DAC Updated 000 DACA 001 DACB 010 DACC 011 DACD 100 DACE 101 DACF 110 DACG 111 DACH

D[7:0] Output Voltage 0000_0000 GND 0000_0001 (1/256) x REF(1+RNG) : : : : : : : : : : 1111_1111 (255/256) x REF (1+RNG)

c) TLC5628 bit assignments.

Figure 5.14: Eight channel DAC. Adapted from [Texas Instrument].

D1

D0

5.11. APPLICATION: ART PIECE ILLUMINATION SYSTEM – REVISITED

135

5 VDC 220

10K

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

Arduino UNO R3

5VGnd

2N2222

Ground

ANALOG IN 0 123 4 5

R Y B IR sensor

Figure 5.15: IR sensor interface.

unsigned int viewer_sensor_reading; void setup() { pinMode(illumination_output, OUTPUT); } void loop() {

//current value of sensor output

//config. pin 0 for dig. output

//read analog output from //IR sensors

136


viewer_sensor_reading

= analogRead(viewer_sensor);

if(viewer_sensor_reading < 128) { analogWrite(illumination_output,31); } else if(viewer_sensor_reading < 256) { analogWrite(illumination_output,63); } else if(viewer_sensor_reading < 384) { analogWrite(illumination_output,95); } else if(viewer_sensor_reading < 512) { analogWrite(illumination_output,127); } else if(viewer_sensor_reading < 640) { analogWrite(illumination_output,159); } else if(viewer_sensor_reading < 768) { analogWrite(illumination_output,191); } else if(viewer_sensor_reading < 896) { analogWrite(illumination_output,223); } else { analogWrite(illumination_output,255); } delay(500); }

//0 (off) to 255 (full speed)







//0 (off) to 255 (full speed) //delay 500 ms

//*************************************************************************

5.12. SUMMARY

137

5.12 SUMMARY In this chapter, we presented the differences between analog and digital signals and used this knowledge to discuss three sub-processing steps involved in analog to digital converters: sampling, quantization, and encoding. We also presented the quantization errors and the data rate associated with the ADC process. The dynamic range of an analog-to-digital converter, one of the measures to describe a conversion process, was also presented. We then presented the successive-approximation converter. Transducer interface design concepts were then discussed along with supporting information on operational amplifier configurations. We then reviewed the operation, registers, and actions required to program the ADC system aboard the ATmega328. We concluded the chapter with a discussion of the ADC process and an implementation using a multi-channel DAC connected to the ATmega328 SPI system.

5.13 REFERENCES • Atmel 8-bit AVR Microcontroller with 16K Bytes In-System Programmable Flash, ATmega328, ATmega328L, data sheet: 2466L-AVR-06/05, Atmel Corporation, 2325 Orchard Parkway, San Jose, CA 95131. • Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025 • Roland Thomas and Albert Rosa, The Analysis and Design of Linear Circuits, Fourth Edition, Wiley & Sons, Inc., New York, 2003. • M.A. Hollander, editor, Electrical Signals and Systems, Fourth Edition, McGraw-Hill Companies, Inc, 1999. • Daniel Pack and Steven Barrett, Microcontroller Theory and Applications: HC12 and S12, Prentice Hall, 2ed, Upper Saddle River, New Jersey 07458, 2008. • Alan Oppenheim and Ronald Schafer, Discrete-time Signal Processing, Second Edition, Prentice Hall, Upper Saddle River, New Jersey, 1999. • John Enderle, Susan Blanchard, and Joseph Bronzino, Introduction to Biomedical Engineering, Academic Press, 2000. • L. Faulkenberry, An Introduction to Operational Amplifiers, John Wiley & Sons, New York, 1977.

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• P. Horowitz and W. Hill, The Art of Electronics, Cambridge University Press, 1989. • L. Faulkenberry, Introduction to Operational Amplifiers with Linear Integrated Circuit Applications, 1982. • D. Stout and M. Kaufman, Handbook of Operational Amplifier Circuit Design McGraw-Hill Book Company, 1976. • S. Franco, Design with Operational Amplifiers and Analog Integrated Circuits, third edition, McGraw-Hill Book Company, 2002. • TLC5628C, TLC5628I Octal 8-bit Digital-to-Analog Converters, Texas Instruments, Dallas, TX, 1997.

5.14 CHAPTER PROBLEMS 1. Given a sinusoid with 500 Hz frequency, what should be the minimum sampling frequency for an analog-to-digital converter, if we want to faithfully reconstruct the analog signal after the conversion? 2. If 12 bits are used to quantize a sampled signal, what is the number of available quantized levels? What will be the resolution of such a system if the input range of the analog-to-digital converter is 10V? 3. Given the 12 V input range of an analog-to-digital converter and the desired resolution of 0.125 V, what should be the minimum number of bits used for the conversion? 4. Investigate the analog-to-digital converters in your audio system. Find the sampling rate, the quantization bits, and the technique used for the conversion. 5. A flex sensor provides 10K ohm of resistance for 0 degrees flexure and 40K ohm of resistance for 90 degrees of flexure. Design a circuit to convert the resistance change to a voltage change (Hint: consider a voltage divider). Then design a transducer interface circuit to convert the output from the flex sensor circuit to voltages suitable for the ATmega328 ADC system. 6. If an analog signal is converted by an analog-to-digital converter to a binary representation and then back to an analog voltage using a DAC, will the original analog input voltage be the same as the resulting analog output voltage? Explain. 7. Derive each of the characteristic equations for the classic operation amplifier configurations provided in Figure 5.4. 8. If a resistor was connected between the non-inverting terminal and ground in the inverting amplifier configuration of Figure 5.4a), how would the characteristic equation change?


139

9. A photodiode provides a current proportional to the light impinging on its active area. What classic operational amplifier configuration should be used to current the diode output to a voltage? 10. Does the time to convert an analog input signal to a digital representation vary in a successiveapproximation converter relative to the magnitude of the input signal?

141

CHAPTER

6

Interrupt Subsystem Objectives: After reading this chapter, the reader should be able to • Understand the need of a microcontroller for interrupt capability. • Describe the general microcontroller interrupt response procedure. • Describe the ATmega328 interrupt features. • Properly configure and program an interrupt event for the ATmega328 in C. • Properly configure and program an interrupt event for the Arduino UNO R3 using built-in features of the Arduino Development Environment. • Use the interrupt system to implement a real time clock. • Employ the interrupt system as a component in an embedded system.

6.1

OVERVIEW

A microcontroller normally executes instructions in an orderly fetch-decode-execute sequence as dictated by a user-written program as shown in Figure 6.1. However, the microcontroller must be equipped to handle unscheduled (although planned), higher priority events that might occur inside or outside the microcontroller.To process such events, a microcontroller requires an interrupt system. The interrupt system onboard a microcontroller allows it to respond to higher priority events. Appropriate responses to these events may be planned, but we do not know when these events will occur. When an interrupt event occurs, the microcontroller will normally complete the instruction it is currently executing and then transition program control to interrupt event specific tasks. These tasks, which resolve the interrupt event, are organized into a function called an interrupt service routine (ISR). Each interrupt will normally have its own interrupt specific ISR. Once the ISR is complete, the microcontroller will resume processing where it left off before the interrupt event occurred. In this chapter, we discuss the ATmega328 interrupt system in detail. We provide several examples on how to program an interrupt in C and also using the built-in features of the Arduino Development Environment.

142

6. INTERRUPT SUBSYSTEM

Fetch

Interrupt Service Routine

Decode

Execute

Figure 6.1: Microcontroller Interrupt Response.

6.2

ATMEGA328 INTERRUPT SYSTEM

The ATmega328 is equipped with a powerful and flexible complement of 26 interrupt sources.Two of the interrupts originate from external interrupt sources while the remaining 24 interrupts support the efficient operation of peripheral subsystems aboard the microcontroller. The ATmega328 interrupt sources are shown in Figure 6.2. The interrupts are listed in descending order of priority. As you can see, the RESET has the highest priority, followed by the external interrupt request pins INT0 (pin 4) and INT1 (pin 5). The remaining interrupt sources are internal to the ATmega328. When an interrupt occurs, the microcontroller completes the current instruction, stores the address of the next instruction on the stack, and starts executing instructions in the designated interrupt service routine (ISR) corresponding to the particular interrupt source. It also turns off the interrupt system to prevent further interrupts while one is in progress. The execution of the ISR is performed by loading the beginning address of the interrupt service routine specific for that interrupt into the program counter. The interrupt service routine will then commence. Execution of

143 6.2. ATMEGA328 INTERRUPT SYSTEM

Vector 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 Address 0x0000 0x0002 0x0004 0x0006 0x0008 0x000A 0x000C 0x000E 0x0010 0x0012 0x0014 0x0016 0x0018 0x001A 0x001C 0x001E 0x0020 0x0022 0x0024 0x0026 0x0028 0x002A 0x002C 0x002E 0x0030 0x0032 Source RESET INT0 INT1 PCINT0 PCINT1 PCINT2 WDT TIMER2 COMPA TIMER2 COMPB TIMER2 OVF TIMER1 CAPT TIMER1 COMPA TIMER1 COMPB TIMER1 OVF TIMER0 COMPA TIMER0 COMPB TIMER0 OVF SPI, STC USART, RX USART, UDRE USART, TX ADC EE READY ANALOG COMP TWI SPM READY

Definition AVR-GCC ISR name External pin, power-on reset, brown-out reset, watchdog system reset INT0_vect External interrupt request 0 INT1_vect External interrupt request 1 PCINT0_vect Pin change interrupt request 0 PCINT1_vect Pin change interrupt request 1 PCINT2_vect Pin change interrupt request 2 WDT_vect Watchdog time-out interrupt Timer/Counter2 Compare Match A TIMER2_COMPA_vect Timer/Counter2 Compare Match B TIMER2_COMPB_vect TIMER2_OVF_vect Timer/Counter2 Overflow TIMER1_CAPT_vect Timer/Counter1 Capture Event Timer/Counter1 Compare Match A TIMER1_COMPA_vect Timer/Counter1 Compare Match B TIMER1_COMPB_vect TIMER1_OVF_vect Timer/Counter1 Overflow Timer/Counter0 Compare Match A TIMER0_COMPA_vect Timer/Counter0 Compare Match B TIMER0_COMPB_vect TIMER0_OVF_vect Timer/Counter0 Overflow SPI_STC_vect SPI Serial Transfer Complete USART_RX_vect USART Rx Complete USART_UDRE_vect USART, Data Register Empty USART_TX_vect USART, Tx Complete ADC_vect ADC Conversion Complete EE_READY_vect EEPROM Ready ANALOG_COMP_vect Analog Comparator TWI_vect 2-wire Serial Interface SPM_ready_vect Store Program Memory Ready

Figure 6.2: Atmel AVR ATmega328 Interrupts. (Adapted from figure used with permission of Atmel, Incorporated.)

144


the ISR continues until the return from interrupt instruction (reti) is encountered. Program control then reverts back to the main program.

6.3

INTERRUPT PROGRAMMING

To program an interrupt the user is responsible for the following actions: • Ensure the interrupt service routine for a specific interrupt is tied to the correct interrupt vector address, which points to the starting address of the interrupt service routine. • Ensure the interrupt system has been globally enabled. This is accomplished with the assembly language instruction SEI. • Ensure the specific interrupt subsystem has been locally enabled. • Ensure the registers associated with the specific interrupt have been configured correctly. In the next two examples that follow, we illustrate how to accomplish these steps. We use the ImageCraft ICC AVR compiler which contains excellent support for interrupts. Other compilers have similar features.

6.4

PROGRAMMING INTERRUPTS IN C AND THE ARDUINO DEVELOPMENT ENVIRONMENT

In this section, we provide two representative examples of writing interrupts. We provide both an externally generated interrupt event and also one generated from within the microcontroller. For each type of interrupt, we illustrate how to program it in C and also with the Arduino Development Environment built-in features. For the C examples, we use the ImageCraft ICC AVR compiler. The ImageCraft ICC AVR compiler uses the following syntax to link an interrupt service routine to the correct interrupt vector address: #pragma interrupt_handler timer_handler:4 void timer_handler(void) { : : } As you can see, the #pragma with the reserved word interrupt_handler is used to communicate to the compiler that the routine name that follows is an interrupt service routine. The number that follows the ISR name corresponds to the interrupt vector number in Figure 6.2. The ISR is then written like any other function. It is important that the ISR name used in the #pragma instruction identically matches the name of the ISR in the function body. Since the compiler knows the function is an ISR, it will automatically place the assembly language RETI instruction at the end of the ISR.

6.4. PROGRAMMING INTERRUPTS IN C AND THE ARDUINO ENVIRONMENT

6.4.1

145

EXTERNAL INTERRUPT PROGRAMMING

The external interrupts INT0 (pin 4) and INT1 (pin 5) trigger an interrupt within the ATmega328 when an user-specified external event occurs at the pin associated with the specific interrupt. Interrupts INT0 and INT1 may be triggered with a falling or rising edge or a low level signal. The specific settings for each interrupt is provided in Figure 6.3.

External Interrupt Control Register - EICRA ISC11

ISC00 0 INT1 INT0 00: low level 00: low level 01: logic change 01: logic change 10: falling edge 10: falling edge 11: rising edge 11: rising edge

7

ISC10 ISC01

External Interrupt Mask Register - EIMSK INT1 7

INT0 0

0: interrupt disabled 1: interrupt enabled External Interrupt Flag Register - EIFR INTF1 INTF0 7

0 Notes: - INTFx flag sets when corresponding interrupt occurs. - INTFx flag reset by executing ISR or writing logic one to flag.

Figure 6.3: Interrupt INT0 and INT1 Registers.

6.4.1.1 Programming external interrupts in C

Provided below is the code snapshot to configure an interrupt for INT0. In this specific example, an interrupt will occur when a positive edge transition occurs on the ATmega328 INT0 external interrupt pin. //interrupt handler definition

146


#pragma interrupt_handler int0_ISR:2 //function prototypes void int0_ISR(void); void initialize_interrupt0(void);

//************************************************************************* //The following function call should be inserted in the main program to //initialize the INT0 interrupt to respond to a positive edge trigger. //This function should only be called once. : initialize_interrupt_int0(); :

//************************************************************************* //function definitions //************************************************************************* //initialize_interrupt_int0: initializes interrupt INT0. //Note: stack is automatically initialized by the compiler //************************************************************************* void initialize_interrupt_int0(void) { DDRD = 0xFB; PORTD &= ˜0x04; EIMSK = 0x01; EICRA = 0x03; asm("SEI"); }

//initialize interrupt INT0 //set PD2 (int0) as input //disable pullup resistor PD2 //enable INT0 //set for positive edge trigger //global interrupt enable

//*************************************************************************


147

//int0_ISR: interrupt service routine for INT0 //************************************************************************* void int0_ISR(void) { //Insert interrupt specific actions here. } The INT0 interrupt is reset by executing the associated interrupt service routine or writing a logic one to the INTF0 bit in the External Interrupt Flag Register (EIFR). 6.4.1.2 Programming external interrupts using the Arduino Development Environment built-in features

The Arduino Development Environment has four built-in functions to support external the INT0 and INT1 external interrupts [www.arduino.cc]. These are the four functions: • interrupts(). This function enables interrupts. • noInterrupts(). This function disables interrupts. • attachInterrupt(interrupt, function, mode). This function links the interrupt to the appropriate interrupt service routine. • detachInterrupt(interrupt). This function turns off the specified interrupt. The Arduino UNO R3 processing board is equipped with two external interrupts: INT0 on DIGITAL pin 2 and INT1 on DIGITAL pin 3. The attachInterrupt(interrupt, function, mode) function is used to link the hardware pin to the appropriate interrupt service pin.The three arguments of the function are configured as follows: • interrupt. Interrupt specifies the INT interrupt number: either 0 or 1. • function. Function specifies the name of the interrupt service routine. • mode. Mode specifies what activity on the interrupt pin will initiate the interrupt: LOW level on pin, CHANGE in pin level, RISING edge, or FALLING edge. To illustrate the use of these built-in Arduino Development Environment features, we revisit the previous example. //*************************************************************************

148


void setup() { attachInterrupt(0, int0_ISR, RISING); } void loop() { //wait for interrupts } //************************************************************************* //int0_ISR: interrupt service routine for INT0 //************************************************************************* void int0_ISR(void) { //Insert interrupt specific actions here. } //*************************************************************************

6.4.2

INTERNAL INTERRUPT PROGRAMMING

In this example, we use Timer/Counter0 as a representative example on how to program internal interrupts. In the example that follows, we use Timer/Counter0 to provide prescribed delays within our program. We discuss the ATmega328 timer system in detail in the next chapter. Briefly, the Timer/Counter0 is an eight bit timer. It rolls over every time it receives 256 timer clock “ticks.” There is an interrupt associated with the Timer/Counter0 overflow. If activated, the interrupt will occur every time the contents of the Timer/Counter0 transitions from 255 back to 0 count. We can use this overflow interrupt as a method of keeping track of real clock time (hours, minutes, and seconds) within a program. In this specific example, we use the overflow to provide precision program delays. 6.4.2.1 Programming an internal interrupt in C

In this example, the ATmega328 is being externally clocked by a 10 MHz ceramic resonator. The resonator frequency is further divided by 256 using the clock select bits CS[2:1:0] in Timer/Counter


149

Control Register B (TCCR0B). When CS[2:1:0] are set for [1:0:0], the incoming clock source is divided by 256. This provides a clock “tick” to Timer/Counter0 every 25.6 microseconds. Therefore, the eight bit Timer/Counter0 will rollover every 256 clock “ticks” or every 6.55 ms. To create a precision delay, we write a function called delay. The function requires an unsigned integer parameter value indicating how many 6.55 ms interrupts the function should delay. The function stays within a while loop until the desired number of interrupts has occurred. For example, to delay one second the function would be called with the parameter value “153.” That is, it requires 153 interrupts occurring at 6.55 ms intervals to generate a one second delay. The code snapshots to configure the Time/Counter0 Overflow interrupt is provided below along with the associated interrupt service routine and the delay function. //function prototypes****************************************************** //delay specified number 6.55ms void delay(unsigned int number_of_6_55ms_interrupts); void init_timer0_ovf_interrupt(void); //initialize timer0 overf.interrupt

//interrupt handler definition********************************************* //interrupt handler definition #pragma interrupt_handler timer0_interrupt_isr:17

//global variables********************************************************* unsigned int input_delay; //counts number of Timer/Counter0 //Overflow interrupts //main program************************************************************* void main(void) { init_timer0_ovf_interrupt();

//initialize Timer/Counter0 Overflow //interrupt - call once at beginning //of program

: : delay(153); }

//1 second delay

150


//************************************************************************* //int_timer0_ovf_interrupt(): The Timer/Counter0 Overfl. interrupt is being //employed as a time base for a master timer for this project. The ceramic //resonator operating at 10 MHz is divided by 256. //The 8-bit Timer0 register //(TCNT0) overflows every 256 counts or every 6.55 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0B = 0x04; TIMSK0 = 0x01; asm("SEI"); }

//divide timer0 timebase by 256, //overflow occurs every 6.55ms //enable timer0 overflow interrupt //enable global interrupt

//************************************************************************* //timer0_interrupt_isr: //Note: Timer overflow 0 is cleared automatically //when executing the corresponding interrupt handling vector. //************************************************************************* void timer0_interrupt_isr(void) { input_delay++; }

//increment overflow counter

//************************************************************************* //delay(unsigned int num_of_6_55ms_interrupts): this generic delay function //provides the specified delay as the number of 6.55 ms "clock ticks" //from the Timer/Counter0 Overflow interrupt. // //Note: this function is only valid when using a 10 MHz crystal or ceramic //resonator. If a different source frequency is used, the clock //tick delay value must be recalculated. //************************************************************************* void delay(unsigned int number_of_6_55ms_interrupts) {


TCNT0 = 0x00; input_delay = 0;

151

//reset timer0 //reset timer0 overflow counter

while(input_delay <= number_of_6_55ms_interrupts) { ; //wait for spec. number of interpts. } } //************************************************************************* 6.4.2.2 Programming an internal interrupt using the Arduino Development Environment The Arduino Development Environment uses the GNU tool chain and the AVR Libc to compile programs. Internal interrupt configuration uses AVR-GCC conventions. To tie the interrupt event to the correct interrupt service routine, the AVR-GCC interrupt name must be used. These vector names are provided in the right column of Figure 6.2. In the following sketch, the previous example is configured for use with the Arduino Development Environment using AVR-GCC conventions. Also, the timing functions in the previous example assumed a time base of 10 MHz. The Arduino UNO R3 is clocked with a 16 MHz crystal. Therefore, some of the parameters in the sketch were adjusted to account for this difference in time base. //************************************************************************* #include

unsigned int

input_delay;

void setup() { init_timer0_ovf_interrupt(); }

//counts number of Timer/Counter0 //Overflow interrupts

//initialize Timer/Counter0 Overfl.

void loop() { : delay(244); :

//1 second delay

152


} //************************************************************************* // ISR(TIMER0_OVF_vect) - increments counter on every interrupt. //************************************************************************* ISR(TIMER0_OVF_vect) { input_delay++; }

//increment overflow counter

//************************************************************************* //int_timer0_ovf_interrupt(): The Timer/Counter0 Overflow interrupt is //being employed as a time base for a master timer for this project. //The crystal //resonator operating at 16 MHz is divided by 256. //The 8-bit Timer0 register (TCNT0) overflows every 256 counts or every //4.1 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0B = 0x04; //divide timer0 timebase by 256, overflow occurs every 4.1 ms TIMSK0 = 0x01; //enable timer0 overflow interrupt asm("SEI"); //enable global interrupt } //************************************************************************* //delay(unsigned int num_of_4_1ms_interrupts): this generic delay function //provides the specified delay as the number of 4.1 ms "clock ticks" from //the Timer/Counter0 Overflow interrupt. // //Note: this function is only valid when using a 16 MHz crystal or ceramic //resonator. If a different source frequency is used, the clock //tick delay value must be recalculated. //************************************************************************* void delay(unsigned int number_of_4_1ms_interrupts) {

6.5. FOREGROUND AND BACKGROUND PROCESSING

TCNT0 = 0x00; input_delay = 0;

153

//reset timer0 //reset timer0 overflow counter

while(input_delay <= number_of_4_1ms_interrupts) { ; //wait for spec. number of intrpts. } } //*************************************************************************

6.5

FOREGROUND AND BACKGROUND PROCESSING

A microcontroller can only process a single instruction at a time. It processes instructions in a fetchdecode-execute sequence as determined by the program and its response to external events. In many cases, a microcontroller has to process multiple events seemingly simultaneously. How is this possible with a single processor? Normal processing accomplished by the microcontroller is called foreground processing. An interrupt may be used to periodically break into foreground processing, ‘steal’ some clock cycles to accomplish another event called background processing, and then return processor control back to the foreground process. As an example, a microcontroller controlling access for an electronic door must monitor input commands from a user and generate the appropriate pulse width modulation (PWM) signals to open and close the door. Once the door is in motion, the controller must monitor door motor operation for obstructions, malfunctions, and other safety related parameters. This may be accomplished using interrupts. In this example, the microcontroller is responding to user input status in the foreground while monitoring safety related status in the background using interrupts as illustrated in Figure 6.4.

6.6

INTERRUPT EXAMPLES

In this section, we provide several varied examples on using interrupts internal and external to the microcontroller.

6.6.1

REAL TIME CLOCK IN C

A microcontroller only ‘understands’ elapsed time in reference to its timebase clock ticks. To keep track of clock time in seconds, minutes, hours etc., a periodic interrupt may be generated for use as a ‘clock tick’ for a real time clock. In this example, we use the Timer 0 overflow to generate a periodic clock tick very 6.55 ms. The ticks are counted in reference to clock time variables and may be displayed on a liquid crystal display. This is also a useful technique for generating very long delays in a microcontroller.

154

6. INTERRUPT SUBSYSTEM Background Processing

Interrupt - check for obstruction - check for malfunctions - check safety parameters


periodic interrupt


periodic interrupt

Monitor to user input, generate motor control signals, etc.

time

Foreground Processing

Figure 6.4: Interrupt used for background processing. The microcontroller responds to user input status in the foreground while monitoring safety related status in the background using interrupts.

//function prototypes****************************************************** //delay specified number 6.55ms void delay(unsigned int number_of_6_55ms_interrupts); void init_timer0_ovf_interrupt(void);//initialize timer0 overflow interrupt

//interrupt handler definition********************************************* //interrupt handler definition #pragma interrupt_handler timer0_interrupt_isr:17

//global variables********************************************************* unsigned int days_ctr, hrs_ctr, mins_ctr, sec_ctr, ms_ctr; //main program************************************************************* void main(void)

6.6. INTERRUPT EXAMPLES

155

{ day_ctr = 0; hr_ctr = 0; min_ctr = 0; sec_ctr = 0; ms_ctr = 0;

init_timer0_ovf_interrupt();

//initialize Timer/Counter0 Overflow

//interrupt - call once at beginning //of program while(1) { ; } }

//wait for interrupts

//************************************************************************* //int_timer0_ovf_interrupt(): The Timer/Counter0 Overflow interrupt is //being employed as a time base for a master timer for this project. //The ceramic resonator operating at 10 MHz is divided by 256. //The 8-bit Timer0 register (TCNT0) overflows every 256 counts or //every 6.55 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0B = 0x04; //divide timer0 timebase by 256, overfl. occurs every 6.55ms TIMSK0 = 0x01; //enable timer0 overflow interrupt asm("SEI"); //enable global interrupt } //************************************************************************* //timer0_interrupt_isr: //Note: Timer overflow 0 is cleared by hardware when executing the //corresponding interrupt handling vector. //************************************************************************* void timer0_interrupt_isr(void) {

156


//Update millisecond counter ms_ctr = ms_ctr + 1;

if(ms_ctr == 154) { ms_ctr = 0; sec_ctr = sec_ctr + 1; } //Update minute counter if(sec_ctr == 60) { sec_ctr = 0; min_ctr = min_ctr + 1; } //Update hour counter if(min_ctr == 60) { min_ctr = 0; hr_ctr = hr_ctr + 1; } //Update day counter if(hr_ctr == 24) { hr_ctr = 0; day_ctr = day_ctr + 1; } }

//increment ms counter //Update second counter //counter equates to 1000 ms at 154 //reset ms counter //increment second counter

//reset sec counter //increment min counter

//reset min counter //increment hr counter

//reset hr counter //increment day counter

//*************************************************************************

6.6.2

REAL TIME CLOCK USING THE ARDUINO DEVELOPMENT ENVIRONMENT

In this example, we reconfigure the previous example using the Arduino Development Environment. The timing functions in the previous example assumed a time base of 10 MHz. The Arduino UNO


157

R3 is clocked with a 16 MHz crystal. Therefore, some of the parameters in the sketch are adjusted to account for this difference in time base. //************************************************************************* #include //global variables********************************************************* unsigned int days_ctr, hrs_ctr, mins_ctr, sec_ctr, ms_ctr; void setup() { day_ctr = 0; hr_ctr = 0; min_ctr = 0; sec_ctr = 0; ms_ctr = 0; init_timer0_ovf_interrupt(); //init. Timer/Counter0 Overflow } void loop() { : : : }

//wait for interrupts

//************************************************************************* // ISR(TIMER0_OVF_vect) Timer0 interrupt service routine. // //Note: Timer overflow 0 is cleared by hardware when executing the //corresponding interrupt handling vector. //************************************************************************* ISR(TIMER0_OVF_vect) { //Update millisecond counter ms_ctr = ms_ctr + 1;

//increment ms counter //Update second counter //counter equates to 1000 ms at 244

if(ms_ctr == 244) { ms_ctr = 0; sec_ctr = sec_ctr + 1;

//each clock tick is 4.1 ms //reset ms counter //increment second counter

158


} //Update minute counter if(sec_ctr == 60) { sec_ctr = 0; min_ctr = min_ctr + 1; } //Update hour counter if(min_ctr == 60) { min_ctr = 0; hr_ctr = hr_ctr + 1; } //Update day counter if(hr_ctr == 24) { hr_ctr = 0; day_ctr = day_ctr + 1; } }

//reset sec counter //increment min counter

//reset min counter //increment hr counter

//reset hr counter //increment day counter

//************************************************************************* //int_timer0_ovf_interrupt(): The Timer/Counter0 //Overflow interrupt is being employed as a time base for a master timer //for this project. The ceramic resonator operating at 16 MHz is //divided by 256. //The 8-bit Timer0 register (TCNT0) overflows every 256 counts or //every 4.1 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0B = 0x04; //divide timer0 timebase by 256, overfl. occurs every 4.1 ms TIMSK0 = 0x01; //enable timer0 overflow interrupt asm("SEI"); //enable global interrupt }


159

//*************************************************************************

6.6.3

INTERRUPT DRIVEN USART IN C

parity (if used)

status bit 2

status bit 1

b11

b10

b9

b8

b7

byte ID = 1

start bit (byte 2)

parity (if used)

b6

b5

b4

b3

b2

b1

b0

byte ID = 0

start bit (byte 1)

In Chapter 4, we discussed the serial communication capability of the USART in some detail. In the following example, we revisit the USART and use it in an interrupt driven mode. Example. You have been asked to evaluate a new positional encoder technology. The encoder provides 12-bit resolution. The position data is sent serially at 9600 Baud as two sequential bytes as shown in Figure 6.5. The actual encoder is new technology and production models are not available for evaluation.

Figure 6.5: Encoder data format. The position data is sent serially at 9600 Baud as two sequential bytes.

Since the actual encoder is not available for evaluation, another Atmel ATmega328 will be used to send signals in identical format and Baud rate as the encoder. The test configuration is illustrated in Figure 6.6. The ATmega328 on the bottom serves as the positional encoder. The microcontroller is equipped with two pushbuttons at PD2 and PD3. The pushbutton at PD2 provides a debounced input to open a simulated door and increment the positional encoder. The pushbutton at PD3 provides a debounced input to close a simulated door and decrement the positional encoder. The current count of the encoder (eight most significant bits) is fed to a digital-to-analog converter (DAC0808) to provide an analog representation. The positional data from the encoder is sent out via the USART in the format described in Figure 6.5. The top ATmega328 receives the positional data using interrupt driven USART techniques. The current position is converted to an analog signal via the DAC. The transmitted and received signals may be compared at the respective DAC outputs. Provided below is the code for the ATmega328 that serves as the encoder simulator followed by the code for receiving the data. //************************************************************************* //author: Steven Barrett, Ph.D., P.E. //last revised: April 15, 2010 //file: encode.c

Figure 6.6: Encoder test configuration. 100K

1M

470K

(3) 0.1uF

(4)

3K

1uf

VDD

sys reset PD3

100K 3K

Vcc = 5.0 volts 74HC14 4.7 K

0.1uF

PD2 (2)

74HC14

(1)

1uf

sys reset

1M

CL Close (active high)

470K

4.7 K

OP Open (active high) Vcc = 5.0 volts

VDD

USART Receiver

1 PUR - PC6 2 RXD - PD0 3 TXD - PD1 4 PD2 5 PD3 6 PD4 7 Vcc Atmega328 8 GND 9 PB6 10 PB7 11 PD5 12 PD6 13 PD7 14 PB0 PC5 28 PC4 27 PC3 26 PC2 25 PC1 24 PCO 23 GND 22 AREF 21 AVCC 20 PB5 19 PB4 18 PB3 17 PB2 16 PB1 15

Position Encoder Simulator

1 PUR - PC6 PC5 28 2 RXD - PD0 PC4 27 3 TXD - PD1 PC3 26 4 PD2 PC2 25 5 PD3 PC1 24 6 PD4 PCO 23 7 Vcc Atmega328 GND 22 8 GND AREF 21 9 PB6 AVCC 20 10 PB7 PB5 19 11 PD5 PB4 18 12 PD6 PB3 17 13 PD7 PB2 16 14 PB0 PB1 15

VDD

VDD

+5 VDC

(14)

VEE = - 5 VDC

A1(5) (15) A2(6) A3(7) DAC0808 A4(8) (1) A5(9) A6(10) (2) A7(11) A8(12) (4) (16) (3)

(13)

+5 VDC

VEE = - 5 VDC

(14) A1(5) (15) A2(6) A3(7) DAC0808 A4(8) (1) A5(9) A6(10) (2) A7(11) A8(12) (4) (16) (3)

(13)

1K

1K

1K

1K

(3)

(2)

2K

(3)

(2)

2K

(4)-5VDC

+5VDC (7) (6)

TL071

400

(4)-5VDC

+5VDC (7) (6)

Vref = 5 VDC

TL071

400

Vref = 5 VDC

160 6. INTERRUPT SUBSYSTEM


161

//target controller: ATMEL ATmega328 // //ATmega328 clock source: internal 8 MHz clock // //ATMEL AVR ATmega328PV Controller Pin Assignments //Chip Port Function I/O Source/Dest Asserted Notes // //Pin 1 to system reset circuitry //Pin 2 PD0: USART receive pin (RXD) //Pin 3 PD1: USART transmit pin (TXD) //Pin 4 PD2 to active high RC debounced switch - Open //Pin 5 PD3 to active high RC debounced switch - Close //Pin 7 Vcc - 1.0 uF to ground //Pin 8 Gnd //Pin 9 PB6 to pin A7(11) on DAC0808 //Pin 10 PB7 to pin A8(12) on DAC0808 //Pin 14 PB0 to pin A1(5) on DAC0808 //Pin 15 PB1 to pin A2(6) on DAC0808 //Pin 16 PB2 to pin A3(7) on DAC0808 //Pin 17 PB3 to pin A4(8) on DAC0808 //Pin 18 PB4 to pin A5(9) on DAC0808 //Pin 19 PB5 to pin A6(10) on DAC0808 //Pin 20 AVCC to 5 VDC //Pin 21 AREF to 5 VDC //Pin 22 Ground //************************************************************************* //include files************************************************************ #include #include //function prototypes****************************************************** //delay specified number 6.55ms int void initialize_ports(void); void USART_init(void); void USART_TX(unsigned char data);

//initializes ports

//main program*************************************************************

162


//global unsigned unsigned unsigned

variables char old_PORTD = 0x08; char new_PORTD; int door_position = 0;

void main(void) { initialize_ports(); USART_init();

//present value of PORTD //new values of PORTD

//return LED configuration to default

//main activity loop - checks PORTD to see if either PD2 (open) //or PD3 (close) was depressed. //If either was depressed the program responds.

while(1) { _StackCheck(); //check for stack overflow read_new_input(); //read input status changes on PORTB } }//end main //Function definitions //************************************************************************* //initialize_ports: provides initial configuration for I/O ports //************************************************************************* void initialize_ports(void) { //PORTB DDRB=0xff; PORTB=0x00;

//PORTB[7-0] output //initialize low

//PORTC DDRC=0xff; PORTC=0x00;

//set PORTC[7-0] as output //initialize low

//PORTD


DDRD=0xf2; PORTD=0x00; }

163

//set PORTD[7-4, 0] as output //initialize low

//************************************************************************* //************************************************************************* //read_new_input: functions polls PORTD for a change in status. If status //change has occurred, appropriate function for status change is called //Pin 4 PD2 to active high RC debounced switch - Open //Pin 5 PD3 to active high RC debounced switch - Close //************************************************************************* void read_new_input(void) { unsigned int gate_position; //measure instantaneous position of gate unsigned int i; unsigned char ms_door_position, ls_door_position, DAC_data; new_PORTD = (PIND & 0x0c); //mask all pins but PORTD[3:2] if(new_PORTD != old_PORTD){ switch(new_PORTD){

//process change in PORTD input

case 0x01: //Open while(PIND == 0x04) { //split into two bytes ms_door_position=(unsigned char)(((door_position >> 6) &(0x00FF))|0x01); ls_door_position=(unsigned char)(((door_position << 1) &(0x00FF))&0xFE); //TX data to USART USART_TX(ms_door_position); USART_TX(ls_door_position); //format data for DAC and send to DAC on PORTB DAC_data=(unsigned char)((door_position >> 4)&(0x00FF)); PORTB = DAC_data;

164


//increment position counter if(door_position >= 4095) door_position = 4095; else door_position++; } break; case 0x02: //Close while(PIND == 0x02) { //split into two bytes ms_door_position=(unsigned char)(((door_position >>6) &(0x00FF))|0x01); ls_door_position=(unsigned char)(((door_position <<1) &(0x00FF))&0xFE); //TX data to USART USART_TX(ms_door_position); USART_TX(ls_door_position); //format data for DAC and send to DAC on PORTB DAC_data=(unsigned char)((door_position >> 4)&(0x00FF)); PORTB = DAC_data; //decrement position counter if(door_position <= 0) door_position = 0; else door_position--; } break; default:; } } old_PORTD = new_PORTD; }

//all other cases //end switch(new_PORTD) //end if new_PORTD //update PORTD


165

//************************************************************************* //USART_init: initializes the USART system // //Note: ATmega328 clocked by internal 8 MHz clock //************************************************************************* void USART_init(void) { UCSRA = 0x00; register initialization UCSRB = 0x08; UCSRC = 0x86;

//control //enable transmitter //async, no parity, 1 stop bit, 8 data bits //Baud Rate initialization //8 MHz clock requires UBRR value of 51 // or 0x0033 to achieve 9600 Baud rate

UBRRH = 0x00; UBRRL = 0x33; } //************************************************************************* //USART_transmit: transmits single byte of data //************************************************************************* void USART_transmit(unsigned char data) { while((UCSRA & 0x20)==0x00) //wait for UDRE flag { ; } UDR = data; //load data to UDR for transmission } //************************************************************************* Receive ATmega328 code follows. //************************************************************************* //author: Steven Barrett, Ph.D., P.E. //last revised: April 15, 2010 //file: receive.c //target controller: ATMEL ATmega328

166


// //ATmega328 clock source: internal 8 MHz clock // //ATMEL AVR ATmega328PV Controller Pin Assignments //Chip Port Function I/O Source/Dest Asserted Notes // //Pin 1 to system reset circuitry //Pin 2 PD0: USART receive pin (RXD) //Pin 3 PD1: USART transmit pin (TXD) //Pin 4 PD2 to active high RC debounced switch - Open //Pin 5 PD3 to active high RC debounced switch - Close //Pin 7 Vcc - 1.0 uF to ground //Pin 8 Gnd //Pin 9 PB6 to pin A7(11) on DAC0808 //Pin 10 PB7 to pin A8(12) on DAC0808 //Pin 14 PB0 to pin A1(5) on DAC0808 //Pin 15 PB1 to pin A2(6) on DAC0808 //Pin 16 PB2 to pin A3(7) on DAC0808 //Pin 17 PB3 to pin A4(8) on DAC0808 //Pin 18 PB4 to pin A5(9) on DAC0808 //Pin 19 PB5 to pin A6(10) on DAC0808 //Pin 20 AVCC to 5 VDC //Pin 21 AREF to 5 VDC //Pin 22 Ground //************************************************************************* //include files************************************************************ #include #include #include //EEPROM support functions #pragma data: eeprom unsigned int door_position_EEPROM #pragma data:data

//function prototypes****************************************************** void initialize_ports(void); //initializes ports void InitUSART(void);


167

unsigned char USART_RX(void); //interrupt handler definition #pragma interrupt_handler USART_RX_interrupt_isr: 19 //main program************************************************************* unsigned int door_position = 0; unsigned char data_rx; unsigned int dummy1 = 0x1234; unsigned int keep_going =1; unsigned int loop_counter = 0; unsigned int ms_position, ls_position; void main(void) { initialize_ports(); USART_init();

//return LED configuration to deflt. //limited startup features //main activity loop - processor will //continually cycle through loop //waiting for USART data

while(1) { //continuous loop waiting for //interrupts _StackCheck(); } }//end main

//check for stack overflow

//Function definitions //************************************************************************* //initialize_ports: provides initial configuration for I/O ports //************************************************************************* void initialize_ports(void) { //PORTB

168


DDRB=0xff; PORTB=0x00;

//PORTB[7-0] output //initialize low


//set PORTC[7-0] as output //initialize low

//PORTD DDRD=0xff; PORTD=0x00; }

//set PORTD[7-0] as output //initialize low

//************************************************************************* //USART_init: initializes the USART system // //Note: ATmega328 clocked by internal 8 MHz clock //************************************************************************* void USART_init(void) { UCSRA = 0x00; register initialization UCSRB = 0x08; UCSRC = 0x86;

//control //enable transmitter //async, no parity, 1 stop bit, 8 data bits //Baud Rate initialization //8 MHz clock requires UBRR value of 51 // or 0x0033 to achieve 9600 Baud rate

UBRRH = 0x00; UBRRL = 0x33; } //************************************************************************* //USART_RX_interrupt_isr //************************************************************************* void USART_RX_interrupt_isr(void) { unsigned char data_rx, DAC_data; unsigned int ls_position, ms_position;


//Receive USART data data_rx = UDR; //Retrieve door position data from EEPROM EEPROM_READ((int) &door_position_EEPROM, door_position); //Determine which byte to update if((data_rx & 0x01)==0x01) { ms_position = data_rx; //Update bit 7 if((ms_position & 0x0020)==0x0020) door_position = door_position | 0x0080; else door_position = door_position & 0xff7f; //Update remaining bits ms_position = ((ms_position<<6) & 0x0f00); //shift left 6--blank other bits door_position = door_position & 0x00ff; door_position = door_position | ms_position; } else { ls_position = data_rx;

//Byte ID = 1

//Test for logic 1 //Set bit 7 to 1 //Reset bit 7 to 0

//Blank ms byte //Update ms byte //Byte ID = 0

//Update ls_position //Shift right 1-blank ls_position = ((ls_position >> 1) & 0x007f); //other bits if((door_position & 0x0080)==0x0080) //Test bit 7 of curr position ls_position = ls_position | 0x0080; else ls_position = ls_position & 0xff7f; door_position = door_position & 0xff00; door_position = door_position | ls_position; }

//Set bit 7 to logic 1 //Reset bit 7 to 0 //Blank ls byte //Update ls byte

169

170


//Store door position data to EEPROM EEPROM_WRITE((int) &door_position_EEPROM, door_position);

//format data for DAC and send to DAC on PORT C DAC_data=(unsigned char)((door_position >> 4)&(0x00FF)); PORTB= DAC_data; } //************************************************************************* //end of file //*************************************************************************

6.7

SUMMARY

In this chapter, we provided an introduction to the interrupt features available aboard the ATmega328 and the Arduino UNO R3 processing board. We also discussed how to program an interrupt for proper operation and provided representative samples for an external interrupt and an internal interrupt.

6.8

REFERENCES

• Atmel 8-bit AVR Microcontroller with 4/8/16/32K Bytes In-System Programmable Flash, ATmega48PA, 88PA, 168PA, 328P data sheet: 8161D-AVR-10/09, Atmel Corporation, 2325 Orchard Parkway, San Jose, CA 95131. • Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025


6.9

171

CHAPTER PROBLEMS

1. What is the purpose of an interrupt? 2. Describe the flow of events when an interrupt occurs. 3. Describe the interrupt features available with the ATmega328. 4. Describe the built-in interrupt features available with the Arduino Development Environment. 5. What is the interrupt priority? How is it determined? 6. What steps are required by the system designer to properly configure an interrupt? 7. How is the interrupt system turned “ON” and “OFF”? 8. A 10 MHz ceramic resonator is not available. Redo the example of the Timer/Counter0 Overflow interrupt provided with a timebase of 1 MHz and 8 MHz. 9. What is the maximum delay that may be generated with the delay function provided in the text without modification? How could the function be modified for longer delays? 10. In the text, we provided a 24 hour timer (hh:mm:ss:ms) using the Timer/Counter0 Overflow interrupt. What is the accuracy of the timer? How can it be improved? 11. Adapt the 24 hour timer example to generate an active high logic pulse on a microcontroller pin of your choice for three seconds. The pin should go logic high three weeks from now. 12. What are the concerns when using multiple interrupts in a given application? 13. How much time can background processing relative to foreground processing be implemented? 14. What is the advantage of using interrupts over polling techniques? 15. Can the USART transmit and interrupt receive system provided in the chapter be adapted to operate in the Arduino Development Environment? Explain in detail.

173

CHAPTER

7

Timing Subsystem Objectives: After reading this chapter, the reader should be able to • Explain key timing system related terminology. • Compute the frequency and the period of a periodic signal using a microcontroller. • Describe functional components of a microcontroller timer system. • Describe the procedure to capture incoming signal events. • Describe the procedure to generate time critical output signals. • Describe the timing related features of the Atmel ATmega328. • Describe the four operating modes of the Atmel ATmega328 timing system. • Describe the register configurations for the ATmega328’s Timer 0, Timer 1, and Timer 2. • Program the Arduino UNO R3 using the built-in timer features of the Arduino Development Environment. • Program the ATmega328 timer system for a variety of applications using C.

7.1

OVERVIEW

One of the most important reasons for using microcontrollers is their capability to perform time related tasks. In a simple application, one can program a microcontroller to turn on or turn off an external device at a specific time. In a more involved application, we can use a microcontroller to generate complex digital waveforms with varying pulse widths to control the speed of a DC motor. In this chapter, we review the capabilities of the Atmel ATmega328 microcontroller to perform time related functions. We begin with a review of timing related terminology. We then provide an overview of the general operation of a timing system followed by the timing system features aboard the ATmega328. Next, we present a detailed discussion of each of its timing channels: Timer 0, Timer 1, and Timer 2 and their different modes of operation. We then review the built-in timing functions of the Arduino Development Environment and conclude the chapter with a variety of examples.

174

7. TIMING SUBSYSTEM

7.2

TIMING RELATED TERMINOLOGY

In this section, we review timing related terminology including frequency, period, and duty cycle.

7.2.1

FREQUENCY

Consider signal x(t) that repeats itself. We call this signal periodic with period T, if it satisfies x(t) = x(t + T ). To measure the frequency of a periodic signal, we count the number of times a particular event repeats within a one second period. The unit of frequency is the Hertz or cycles per second. For example, a sinusoidal signal with the 60 Hz frequency means that a full cycle of a sinusoid signal repeats itself 60 times each second or every 16.67 ms.

7.2.2

PERIOD

The reciprocal of frequency is the period of a waveform. If an event occurs with a rate of 1 Hz, the period of that event is 1 second. To find a period, given the frequency of a signal, or vice versa, we simply need to remember their inverse relationship f = T1 where f and T represent a frequency and the corresponding period, respectively. Both periods and frequencies of signals are often used to specify timing constraints of microcontroller-based systems. For example, when your car is on a wintery road and slipping, the engineers who designed your car configured the anti-slippage unit to react within some millisecond period, say 20 milliseconds. The constraint then forces the design team that monitors the slippage to program their monitoring system to check a slippage at a rate of 50 Hz.

7.2.3

DUTY CYCLE

In many applications, periodic pulses are used as control signals. A good example is the use of a periodic pulse to control a servo motor. To control the direction and sometimes the speed of a motor, a periodic pulse signal with a changing duty cycle over time is used. The periodic pulse signal shown in Figure 7.1(a) is on for 50 percent of the signal period and off for the rest of the period. The pulse shown in (b) is on for only 25 percent of the same period as the signal in (a) and off for 75 percent of the period. The duty cycle is defined as the percentage of the period a signal is on or logic high. Therefore, we call the signal in Figure 7.1(a) as a periodic pulse signal with a 50 percent duty cycle and the corresponding signal in (b), a periodic pulse signal with a 25 percent duty cycle.

7.3

TIMING SYSTEM OVERVIEW

The heart of the timing system is the time base. The time base’s frequency of a microcontroller is used to generate a baseline clock signal. For a timer system, the system clock is used to update the contents of a special register called a free running counter. The job of a free running counter is to

7.3. TIMING SYSTEM OVERVIEW

175

50 %

100 % (a)

25 %

100 % (b) Figure 7.1: Two signals with the same period but different duty cycles.The top figure (a) shows a periodic signal with a 50% duty cycle and the lower figure (b) displays a periodic signal with a 25% duty cycle.

count up (increment) each time it sees a rising edge (or a falling edge) of a clock signal. Thus, if a clock is running at the rate of 2 MHz, the free running counter will count up or increment each 0.5 microseconds. All other timer related units reference the contents of the free running counter to perform input and output time related activities: measurement of time periods, capture of timing events, and generation of time related signals. The ATmega328 may be clocked internally using a user-selectable resistor capacitor (RC) time base or it may be clocked externally. The RC internal time base is selected using programmable fuse bits. You may choose an internal fixed clock operating frequency of 1, 2, 4 or 8 MHz. To provide for a wider range of frequency selections an external time source may be used. The external time sources, in order of increasing accuracy and stability, are an external RC network, a ceramic resonator, and a crystal oscillator. The system designer chooses the time base frequency and clock source device appropriate for the application at hand. As previously mentioned, the maximum operating frequency of the ATmega328P with a 5 VDC supply voltage is 20 MHz. The Arduino UNO R3 processing board is equipped with a 16 MHz crystal oscillator time base.

176

7. TIMING SUBSYSTEM

For input time related activities, all microcontrollers typically have timer hardware components that detect signal logic changes on one or more input pins. Such components rely on a free running counter to capture external event times. We can use such ability to measure the period of an incoming signal, the width of a pulse, and the time of a signal logic change. For output timer functions, a microcontroller uses a comparator, a free running counter, logic switches, and special purpose registers to generate time related signals on one or more output pins. A comparator checks the value of the free running counter for a match with the contents of another special purpose register where a programmer stores a specified time in terms of the free running counter value. The checking process is executed at each clock cycle and when a match occurs, the corresponding hardware system induces a programmed logic change on a programmed output port pin. Using such capability, one can generate a simple logic change at a designated time incident, a pulse with a desired time width, or a pulse width modulated signal to control servo or Direct Current (DC) motors. You can also use the timer input system to measure the pulse width of an aperiodic signal. For example, suppose that the times for the rising edge and the falling edge of an incoming signal are 1.5 sec and 1.6 sec, respectively. We can use these values to easily compute the pulse width of 0.1 second. The second overall goal of the timer system is to generate signals to control external devices. Again an event simply means a change of logic states on an output pin of a microcontroller at a specified time. Now consider Figure 7.2. Suppose an external device connected to the microcontroller requires a pulse signal to turn itself on. Suppose the particular pulse the external device needs is 2 millisecond wide. In such situations, we can use the free running counter value to synchronize the time of desired logic state changes. Naturally, extending the same capability, we can also generate a periodic pulse with a fixed duty cycle or a varying duty cycle. From the examples we discussed above, you may have wondered how a microcontroller can be used to compute absolute times from the relative free running counter values, say 1.5 second and 1.6 second. The simple answer is that we can not do so directly. A programmer must use the system clock values and derive the absolute time values. Suppose your microcontroller is clocked by a 2 MHz signal and the system clock uses a 16-bit free running counter. For such a system, each clock period represents 0.5 microsecond and it takes approximately 32.78 milliseconds to count from 0 to 216 (65,536). The timer input system then uses the clock values to compute frequencies, periods, and pulse widths. For example, suppose you want to measure a pulse width of an incoming aperiodic signal. If the rising edge and the falling edge occurred at count values $0010 and $0114, 1 can you find the pulse width when the free running counter is counting at 2 MHz? Let’s first convert the two values into their corresponding decimal values, 276 and 16. The pulse width of the signal in the number of counter value is 260. Since we already know how long it takes for the system to increment by one, we can readily compute the pulse width as 260 × 0.5 microseconds = 130 microseconds.

1The $ symbol represents that the following value is in a hexadecimal form.

7.3. TIMING SYSTEM OVERVIEW

Special Storage Register

Comparator

Timer Output Flag

Programmed Event - Toggle - Logic high - Logic low

Timer Output Interrupt System

Physical Output Pin

177

Free-Running Counter

Figure 7.2: A diagram of a timer output system.

Our calculations do not take into account time increments lasting longer than the rollover time of the counter. When a counter rolls over from its maximum value back to zero, a status flag is set to notify the processor of this event. The rollover events may be counted to correctly determine the overall elapsed time of an event. To calculate the total elapsed time of an event; the event start time, stop time, and the number of timer overflows (n) that occurred between the start time and stop time must be known. Elapsed time may be calculated using: elapsed clock ticks = (n × 2b ) + (stop count − start count) [clock ticks]

elapsed time = (elapsed clock ticks) × (F RC clock period) [seconds] In this first equation, “n” is the number of Timer Overflow Flag (TOF) events that occur between the start and stop events and “b” is the number of bits in the timer counter. The equation

178

7. TIMING SUBSYSTEM

yields the elapsed time in clock ticks. To convert to seconds the number of clock ticks are multiplied by the period of the clock source of the free running counter.

7.4

APPLICATIONS

In this section, we consider some important uses of the timer system of a microcontroller to (1) measure an input signal timing event, termed input capture, (2) to count the number of external signal occurrences, (3) to generate timed signals — termed output compare, and, finally, (4) to generate pulse width modulated signals. We first start with a case of measuring the time duration of an incoming signal.

7.4.1

INPUT CAPTURE — MEASURING EXTERNAL TIMING EVENT

In many applications, we are interested in measuring the elapsed time or the frequency of an external event using a microcontroller. Using the hardware and functional units discussed in the previous sections, we now present a procedure to accomplish the task of computing the frequency of an incoming periodic signal. Figure 7.3 shows an incoming periodic signal to our microcontroller. Microcontroller Timer Input Port

Timer Output Port

External Device

Figure 7.3: Use of the timer input and output systems of a microcontroller. The signal on top is fed into a timer input port. The captured signal is subsequently used to compute the input signal frequency. The signal on the bottom is generated using the timer output system. The signal is used to control an external device.

The first necessary step for the current task is to turn on the timer system. To reduce power consumption a microcontroller usually does not turn on all of its functional systems after reset until they are needed. In addition to a separate timer module, many microcontroller manufacturers allow a programmer to choose the rate of a separate timer clock that governs the overall functions of a timer module. Once the timer is turned on and the clock rate is selected, a programmer must configure the physical port to which the incoming signal arrives. This step is done using a special input timer port

7.4. APPLICATIONS

179

configuration register. The next step is to program the input event to capture. In our current example, we should capture two consecutive rising edges or falling edges of the incoming signal. Again, the programming portion is done by storing an appropriate setup value to a special register. Now that the input timer system is configured appropriately, you now have two options to accomplish the task. The first one is the use of a polling technique; the microcontroller continuously polls a flag, which holds a logic high signal when a programmed event occurs on the physical pin. Once the microcontroller detects the flag, it needs to clear the flag and record the time when the flag was set using another special register that captures the time of the associated free running counter value. The program needs to continue to wait for the next flag, which indicates the end of one period of the incoming signal. A programmer then needs to record the newly acquired captured time represented in the form of a free running counter value again. The period of the signal can now be computed by computing the time difference between the two captured event times, and, based on the clock speed of the microcontroller’s timer system, the programmer can compute the actual time changes and consequently the frequency of the signal. In many cases, a microcontroller can’t afford the time to poll for one event. Such situation introduces the second method: interrupt systems. Most microcontroller manufacturers have developed built-in interrupt systems with their timer input modules. Instead of continuously polling for a flag, a microcontroller performs other tasks and relies on its interrupt system to detect the programmed event. The task of computing the period and the frequency is the same as the first method, except that the microcontroller will not be tied down to constantly checking the flag, increasing the efficient use of the microcontroller resources. To use interrupt systems, of course, we must pay the price by appropriately configuring the interrupt systems to be triggered when a desired event is detected. Typically, additional registers must be configured, and a special program called an interrupt service routine must be written. Suppose that for an input capture scenario the two captured times for the two rising edges are $1000 and $5000, respectively. Note that these values are not absolute times but the representations of times reflected as the values of the free running counter. The period of the signal is $4000 or 16384 in a decimal form. If we assume that the timer clock runs at 10 MHz, the period of the signal is 1.6384 msec, and the corresponding frequency of the signal is approximately 610.35 Hz.

7.4.2

COUNTING EVENTS

The same capability of measuring the period of a signal can also be used to simply count external events. Suppose we want to count the number of logic state changes of an incoming signal for a given period of time. Again, we can use the polling technique or the interrupt technique to accomplish the task. For both techniques, the initial steps of turning on a timer and configuring a physical input port pin are the same. In this application, however, the programmed event should be any logic state changes instead of looking for a rising or a falling edge as we have done in the previous section. If the polling technique is used, at each event detection, the corresponding flag must be cleared and

180

7. TIMING SUBSYSTEM

a counter must be updated. If the interrupt technique is used, one must write an interrupt service routine within which the flag is cleared and a counter is updated.

7.4.3

OUTPUT COMPARE — GENERATING TIMING SIGNALS TO INTERFACE EXTERNAL DEVICES

In the previous two sections, we considered two applications of capturing external incoming signals. In this subsection and the next one, we consider how a microcontroller can generate time critical signals for external devices. Suppose in this application, we want to send a signal shown in Figure 7.3 to turn on an external device. The timing signal is arbitrary but the application will show that a timer output system can generate any desired time related signals permitted under the timer clock speed limit of the microcontroller. Similar to the use of the timer input system, one must first turn on the timer system and configure a physical pin as a timer output pin using special registers. In addition, one also needs to program the desired external event using another special register associated with the timer output system. To generate the signal shown in Figure 7.3, one must compute the time required between the rising and the falling edges. Suppose that the external device requires a pulse which is 2 milliseconds wide to be activated. To generate the desired pulse, one must first program the logic state for the particular pin to be low and set the time value using a special register with respect to the contents of the free running counter. As was mentioned in Section 5.2, at each clock cycle, the special register contents are compared with the contents of the free running counter and when a match occurs, the programmed logic state appears on the designated hardware pin. Once the rising edge is generated, the program then must reconfigure the event to be a falling edge (logic state low) and change the contents of the special register to be compared with the free running counter. For the particular example in Figure 7.3, let’s assume that the main clock runs at 2 MHz, the free running counter is a 16 bit counter, and the name of the special register (16 bit register) where we can put appropriate values is output timer register. To generate the desired pulse, we can put $0000 first to the output timer register, and after the rising edge has been generated, we need to change the program event to a falling edge and put $0FA0 or 4000 in decimal to the output timer register. As was the case with the input timer system module, we can use output timer system interrupts to generate the desired signals as well.

7.4.4

INDUSTRIAL IMPLEMENTATION CASE STUDY (PWM)

In this section, we discuss a well-known method to control the speed of a DC motor using a pulse width modulated (PWM) signal. The underlying concept is as follows. If we turn on a DC motor and provide the required voltage, the motor will run at its maximum speed. Suppose we turn the motor on and off rapidly, by applying a periodic signal. The motor at some point can not react fast enough to the changes of the voltage values and will run at the speed proportional to the average time the motor was turned on. By changing the duty cycle, we can control the speed of a DC motor as we desire. Suppose again we want to generate a speed profile shown in Figure 7.4. As shown in

7.4. APPLICATIONS

181

[hbt]

Motor Velocity

Speed Profile

Acceleration Period

Constant Speed Period Deceleration Period

Time Pulse Width Modulated Signal

DC Motor GND

Figure 7.4: The figure shows the speed profile of a DC motor over time when a pulse-width-modulated signal is applied to the motor.

the figure, we want to accelerate the speed, maintain the speed, and decelerate the speed for a fixed amount of time. As an example, an elevator control system does not immediately operate the elevator motor at full speed. The elevator motor speed will ramp up gradually from stop to desired speed. As the elevator approaches, the desired floor it will gradually ramp back down to stop. The first task necessary is again to turn on the timer system, configure a physical port, and program the event to be a rising edge. As a part of the initialization process, we need to put $0000 to the output timer register we discussed in the previous subsection. Once the rising edge is generated, the program then needs to modify the event to a falling edge and change the contents of the output timer register to a value proportional to a desired duty cycle. For example, if we want to start off with 25% duty cycle, we need to input $4000 to the register, provided that we are using a 16 bit free running counter. Once the falling edge is generated, we now need to go back and change the event to be a rising edge and the contents of the output timer counter value back to $0000. If we want

182

7. TIMING SUBSYSTEM

to continue to generate a 25% duty cycle signal, then we must repeat the process indefinitely. Note that we are using the time for a free running counter to count from $0000 to $FFFF as one period. Now suppose we want to increase the duty cycle to 50% over 1 sec and that the clock is running at 2 MHz. This means that the free running counter counts from $0000 to $FFFF every 32.768 milliseconds, and the free running counter will count from $0000 to $FFFF approximately 30.51 times over the period of one second. That is we need to increase the pulse width from $4000 to $8000 in approximately 30 turns, or approximately 546 clock counts every turn. This technique may be used to generate any desired duty cycle.

7.5

OVERVIEW OF THE ATMEL ATMEGA328 TIMER SYSTEM

The Atmel ATmega328 is equipped with a flexible and powerful three channel timing system. The timer channels are designated Timer 0,Timer 1, and Timer 2. In this section, we review the operation of the timing system in detail. We begin with an overview of the timing system features followed by a detailed discussion of timer channel 0. Space does not permit a complete discussion of the other two timing channels; we review their complement of registers and highlight their features not contained in our discussion of timer channel 0. The information provided on timer channel 0 is readily adapted to the other two channels. The features of the timing system are summarized in Figure 7.5.Timer 0 and 2 are 8-bit timers; whereas, Timer 1 is a 16-bit timer. Each timing channel is equipped with a prescaler. The prescaler is used to subdivide the main microcontroller clock source (designated fclk_I /O in upcoming diagrams) down to the clock source for the timing system (clkT n ). Each timing channel has the capability to generate pulse width modulated signals, generate a periodic signal with a specific frequency, count events, and generate a precision signal using the output compare channels. Additionally, Timer 1 is equipped with the Input Capture feature. All of the timing channels may be configured to operate in one of four operational modes designated : Normal, Clear Timer on Compare Match (CTC), Fast PWM, and Phase Correct PWM. We provide more information on these modes shortly.

7.6

TIMER 0 SYSTEM

In this section, we discuss the features, overall architecture, modes of operation, registers, and programming of Timer 0. This information may be readily adapted to Timer 1 and Timer 2. A Timer 0 block diagram is shown in Figure 7.6. The clock source for Timer 0 is provided via an external clock source at the T0 pin (PD4) of the microcontroller. Timer 0 may also be clocked internally via the microcontroller’s main clock (fclk_I /O ). This clock frequency may be too rapid for many applications. Therefore, the timing system is equipped with a prescaler to subdivide the main clock frequency down to timer system frequency (clkT n ). The clock source for Timer 0 is selected using the CS0[2:0] bits contained in the Timer/Counter Control Register B (TCCR0B).

7.6. TIMER 0 SYSTEM

Timer 0 - 8-bit timer/counter - 10-bit clock prescaler - Functions: -- Pulse width modulation -- Frequency generation -- Event counter -- Output compare -- 2 ch - Modes of operation: -- Normal -- Clear timer on compare match (CTC) -- Fast PWM -- Phase correct PWM

Timer 1 - 16-bit timer/counter - 10-bit clock prescaler - Functions: -- Pulse width modulation -- Frequency generation -- Event counter -- Output compare -- 2 ch -- Input capture - Modes of operation: -- Normal -- Clear timer on compare match (CTC) -- Fast PWM -- Phase correct PWM

183

Timer 2 - 8-bit timer/counter - 10-bit clock prescaler - Functions: -- Pulse width modulation -- Frequency generation -- Event counter -- Output compare -- 2 ch - Modes of operation: -- Normal -- Clear timer on compare match (CTC) -- Fast PWM -- Phase correct PWM

Figure 7.5: Atmel timer system overview.

The TCCR0A register contains the WGM0[1:0] bits and the COM0A[1:0] (and B) bits. Whereas, the TCCR0B register contains the WGM0[2] bit.These bits are used to select the mode of operation for Timer 0 as well as tailor waveform generation for a specific application. The timer clock source (clkT n ) is fed to the 8-bit Timer/Counter Register (TCNT0). This register is incremented (or decremented) on each clkT n clock pulse. Timer 0 is also equipped with two 8-bit comparators that constantly compares the numerical content of TCNT0 to the Output Compare Register A (OCR0A) and Output Compare Register B (OCR0B). The compare signal from the 8-bit comparator is fed to the waveform generators. The waveform generators have a number of inputs to perform different operations with the timer system. The BOTTOM signal for the waveform generation and the control logic, shown in Figure 7.6, is asserted when the timer counter TCNT0 reaches all zeroes (0x00). The MAX signal for the control logic unit is asserted when the counter reaches all ones (0xFF). The TOP signal for the waveform generation is asserted by either reaching the maximum count values of 0xFF on the TCNT0 register or reaching the value set in the Output Compare Register 0 A (OCR0A) or B. The setting for the TOP signal will be determined by the Timer’s mode of operation. Timer 0 also uses certain bits within the Timer/Counter Interrupt Mask Register 0 (TIMSK0) and the Timer/Counter Interrupt Flag Register 0 (TIFR0) to signal interrupt related events.

184

7. TIMING SUBSYSTEM

Figure 7.6: Timer 0 block diagram. (Figure used with permission Atmel, Inc.)

7.6.1

MODES OF OPERATION

Each of the timer channels may be set for a specific mode of operation: normal, clear timer on compare match (CTC), fast PWM, and phase correct PWM. The system designer chooses the correct mode for the application at hand. The timer modes of operation are summarized in Figure 7.7. A specific mode of operation is selected using the Waveform Generation Mode bits located in Timer/Control Register A (TCCR0A) and Timer/Control Register B (TCCR0B). 7.6.1.1 Normal Mode

In the normal mode, the timer will continually count up from 0x00 (BOTTOM) to 0xFF (TOP). When the TCNT0 returns to zero on each cycle of the counter the Timer/Counter Overflow Flag

185 7.6. TIMER 0 SYSTEM

Normal Mode

TCNT0

OCR0

OC0

TOP

BOTTOM TOV0

TOP OCR0

TOV0

TOV0

OC0

OC0

OCR0

TOV0

fOC0PWM = fclk_I/O/ (N x 256)

Fast PWM Mode

TCNT0

OC0

Figure 7.7: Timer 0 modes of operation.

TOV0

TOV0

BOTTOM

OC0

OCR0

OC0

OC0

OCR0

TOV0

OCR0

OC0

OC0

OC0

BOTTOM

TOV0

OCR0

fOC0 = (fclk_I/O)/ (2 x N x (1 + OCR0))

Clear Timer on Compare Match (CTC)

OC0

TCNT0 OC0 inter flag

OC0

OCR0

TOP

TOV0

fOC0PWM = fclk_I/O/ (N x 510)

Phase Correct PWM Mode

TCNT0

OC0

186

7. TIMING SUBSYSTEM

(TOV0) will be set. The normal mode is useful for generating a periodic “clock tick” that may be used to calculate elapsed real time or provide delays within a system. We provide an example of this application in Section 5.9. 7.6.1.2 Clear Timer on Compare Match (CTC)

In the CTC mode, the TCNT0 timer is reset to zero every time the TCNT0 counter reaches the value set in Output Compare Register A (OCR0A) or B. The Output Compare Flag A (OCF0A) or B is set when this event occurs. The OCF0A or B flag is enabled by asserting the Timer/Counter 0 Output Compare Math Interrupt Enable (OCIE0A) or B flag in the Timer/Counter Interrupt Mask Register 0 (TIMSK0) and when the I-bit in the Status Register is set to one. The CTC mode is used to generate a precision digital waveform such as a periodic signal or a single pulse. The user must describe the parameters and key features of the waveform in terms of Timer 0 “clock ticks.” When a specific key feature is reached within the waveform the next key feature may be set into the OCR0A or B register. 7.6.1.3 Phase Correct PWM Mode

In the Phase Correct PWM Mode, the TCNT0 register counts from 0x00 to 0xFF and back down to 0x00 continually. Every time the TCNT0 value matches the value set in the OCR0A or B register the OCF0A or B flag is set and a change in the PWM signal occurs. 7.6.1.4 Fast PWM

The Fast PWM mode is used to generate a precision PWM signal of a desired frequency and duty cycle. It is called the Fast PWM because its maximum frequency is twice that of the Phase Correct PWM mode. When the TCNT0 register value reaches the value set in the OCR0A or B register it will cause a change in the PWM output as prescribed by the system designer. It continues to count up to the TOP value at which time the Timer/Counter 0 Overflow Flag is set.

7.6.2

TIMER 0 REGISTERS

A summary of the Timer 0 registers are shown in Figure 7.8. 7.6.2.1 Timer/Counter Control Registers A and B (TCCR0A and TCCR0B) The TCCR0 register bits are used to:

• Select the operational mode of Timer 0 using the Waveform Mode Generation (WGM0[2:0]) bits, • Determine the operation of the timer within a specific mode with the Compare Match Output Mode (COM0A[1:0] or COM0B[1:0] or) bits, and • Select the source of the Timer 0 clock using Clock Select (CS0[2:0]) bits. The bit settings for the TCCR0 register are summarized in Figure 7.9.

7.6. TIMER 0 SYSTEM

187

Timer/Counter Control Register A (TCCR0A) ---

COM0A1 COM0A0 COM0B1 COM0B0

---

WGM01 WGM00

7

0

Timer/Counter Control Register B (TCCR0B) FOC0A FOC0B

---

---

WGM02 CS02

7

CS01

CS00 0

Timer/Counter Register (TCNT0) 7 Output Compare Register A (OCR0A)

0

7

0

Output Compare Register B (OCR0B) 7 Timer/Counter Interrupt Mask Register 0 (TIMSK0) ---

---

---

---

---

OCIE0B OCIE0A TOIE0

7 Timer/Counter Interrupt Flag REgister 0 (TIFR0) ---

---

---

---

---

0

0

OCF0B OCF0A TOV0

7

0

Figure 7.8: Timer 0 registers.

7.6.2.2 Timer/Counter Register(TCNT0) The TCNT0 is the 8-bit counter for Timer 0. 7.6.2.3 Output Compare Registers A and B (OCR0A and OCR0B)

The OCR0A and B registers holds a user-defined 8-bit value that is continuously compared to the TCNT0 register. 7.6.2.4 Timer/Counter Interrupt Mask Register (TIMSK0)

Timer 0 uses the Timer/Counter 0 Output Compare Match Interrupt Enable A and B (OCIE0A and B) bits and the Timer/Counter 0 Overflow Interrupt Enable (TOIE0) bit. When the OCIE0A

188

7. TIMING SUBSYSTEM CS0[2:0] 000 001 010 011 100 101 110 111

Clock Source None clkI/0 clkI/0/8 clkI/0/64 clkI/0/8clkI/0/256 clkI/0/8clkI/0/1024 External clock on T0 (falling edge trigger) External clock on T1 (rising edge trigger) Clock Select


---

---

WGM02 CS02

CS01

CS00

7 Timer/Counter Control Register A (TCCR0A) COM0A1 COM0A0 COM0B1 COM0B0

---

0 ---

WGM01 WGM00

Waveform Generation Mode Mode WGM[02:00] Mode 0 000 Normal 1 001 PWM, Phase Correct 2 010 CTC 3 011 Fast PWM 4 100 Reserved 5 101 PWM, Phase Correct 6 110 Reserved 7 111 Fast PWM Compare Output Mode, non-PWM Mode COM0A[1:0] Description 00 Normal, OC0A disconnected 01 Toggle OC0A on compare match 10 Clear OC0A on compare match 11 Set OC0A on compare match

Compare Output Mode, non-PWM Mode COM0B[1:0] Description 00 Normal, OC0B disconnected 01 Toggle OC0B on compare match 10 Clear OC0B on compare match 11 Set OC0B on compare match

Compare Output Mode, Fast PWM Mode COM0A[1:0] Description 00 Normal, OC0A disconnected 01 WGM02 = 0: normal operation, OC0A disconnected WGM02 = 1: Toggle OC0A on compare match 10 Clear OC0A on compare match, set OC0A at Bottom (non-inverting mode) 11 Set OC0A on compare match, clear OC0A at Bottom (inverting mode)

Compare Output Mode, Fast PWM Mode COM0B[1:0] Description 00 Normal, OC0B disconnected 01 Reserved

Compare Output Mode, Phase Correct PWM


COM0A[1:0] Description 00 Normal, OC0A disconnected 01 WGM02 = 0: normal operation, OC0A disconnected WGM02 = 1: Toggle OC0A on compare match Clear OC0A on compare match, 10 when upcounting. Set OC0A on compare match when down counting Set OC0A on compare match, 11 when upcounting. Set OC0A on compare match when down counting

10

11

Clear OC0B on compare match, set OC0B at Bottom (non-inverting mode) Set OC0B on compare match, clear OC0B at Bottom (inverting mode)

COM0B[1:0] Description 00 Normal, OC0B disconnected 01 Reserved

10

11

Clear OC0B on compare match, when upcounting. Set OC0B on compare match when down counting Set OC0B on compare match, when upcounting. Set OC0B on compare match when down counting

Figure 7.9: Timer/Counter Control Registers A and B (TCCR0A and TCCR0B) bit settings.

7.7. TIMER 1

189

or B bit and the I-bit in the Status Register are both set to one, the Timer/Counter 0 Compare Match interrupt is enabled. When the TOIE0 bit and the I-bit in the Status Register are both set to one, the Timer/Counter 0 Overflow interrupt is enabled. 7.6.2.5 Timer/Counter Interrupt Flag Register 0 (TIFR0) Timer 0 uses the Output Compare Flag A or B (OCF0A and OCF0B) which sets for an output compare match. Timer 0 also uses the Timer/Counter 0 Overflow Flag (TOV0) which sets when Timer/Counter 0 overflows.

7.7

TIMER 1

Timer 1 is a 16-bit timer/counter. It shares many of the same features of the Timer 0 channel. Due to limited space the shared information will not be repeated. Instead, we concentrate on the enhancements of Timer 1 which include an additional output compare channel and also the capability for input capture. The block diagram for Timer 1 is shown in Figure 7.10. As discussed earlier in the chapter, the input capture feature is used to capture the characteristics of an input signal including period, frequency, duty cycle, or pulse length. This is accomplished by monitoring for a user-specified edge on the ICP1 microcontroller pin. When the desired edge occurs, the value of the Timer/Counter 1 (TCNT1) register is captured and stored in the Input Capture Register 1 (ICR1).

7.7.1

TIMER 1 REGISTERS

The complement of registers supporting Timer 1 are shown in Figure 7.11. Each register will be discussed in turn. 7.7.1.1 TCCR1A and TCCR1B registers

The TCCR1 register bits are used to: • Select the operational mode of Timer 1 using the Waveform Mode Generation (WGM1[3:0]) bits, • Determine the operation of the timer within a specific mode with the Compare Match Output Mode (Channel A: COM1A[1:0] and Channel B: COM1B[1:0]) bits, and • Select the source of the Timer 1 clock using Clock Select (CS1[2:0]) bits. The bit settings for the TCCR1A and TCCR1B registers are summarized in Figure 7.12. 7.7.1.2 Timer/Counter Register 1 (TCNT1H/TCNT1L)

The TCNT1 is the 16-bit counter for Timer 1.

190

7. TIMING SUBSYSTEM

Figure 7.10: Timer 1 block diagram. (Figure used with Permission, Atmel,Inc.)

7.7. TIMER 1

Timer/Counter 1 Control Register A (TCCR1A) COM1A1 COM1A0 COM1B1 COM1B0

---

---

WGM11

7 Timer/Counter 1 Control Register B (TCCR1B) ICNC1

ICES1

---

WGM13 WGM12

0

CS12

CS11

7 Timer/Counter 1 Control Register C (TCCR1C) FOC1A FOC1B

---

---

---

WGM10

CS10

0 ---

7

---

--0

Timer Counter1 (TCNT1H/TCNT1L) 15

8

7

0

Output Compare Register 1 A (OCR1AH/OCR1AL) 15

8

7

0

Output Compare Register 1 B (OCR1BH/OCR1BL) 15

8

7

0

Input Capture Register 1 (ICR1H/ICR1L) 15

8

7

0

Timer/Counter Interrupt Mask Register 1 (TIMSK1) ---

---

ICIE1

---

---

OCIE1B OCIE1A TOIE1

7 Timer/Counter 1 Interrupt Flag REgister (TIFR1) ---

---

7 Figure 7.11: Timer 1 registers.

ICF1

---

---

0

OCF1B OCF1A TOV1 0

191

192

7. TIMING SUBSYSTEM CS0[2:0] 000 001 010 011 100 101 110 111

Clock Source None clkI/0 clkI/0/8 clkI/0/64 clkI/0/8clkI/0/256 clkI/0/8clkI/0/1024 External clock on T0 (falling edge trigger) External clock on T1 (rising edge trigger) Clock Select

Timer/Counter 1 Control Register B (TCCR1B) ICNC1

ICES1

---

WGM13 WGM12

CS12

CS11

7 Timer/Counter 1 Control Register A (TCCR1A) COM1A1 COM1A0 COM1B1 COM1B0

---

CS10

0 ---

WGM11

7 Waveform Generation Mode Mode WGM[13:12:11:10] Mode 0 0000 Normal 1 0001 PWM, Phase Correct, 8-bit 2 0010 PWM, Phase Correct, 9-bit 3 0011 PWM, Phase Correct, 10-bit 4 0100 CTC 5 0101 Fast PWM, 8-bit 6 0110 Fast PWM, 9-bit 7 0111 Fast PWM, 10-bit 8 1000 PWM, Phase & Freq Correct 9 1001 PWM, Phase & Freq Correct 10 1010 PWM, Phase Correct 11 1011 PWM, Phase Correct 12 1100 CTC 13 1101 Reserved 14 1110 Fast PWM 15 1111 Fast PWM

WGM10

0 Normal, CTC COMx[1:0] Description 00 Normal, OC1A/1B disconnected 01 Toggle OC1A/1B on compare match 10 Clear OC1A/1B on compare match 11 Set OC1A/1B on compare match PWM, Phase Correct, Phase & Freq Correct COMx[1:0] Description 00 Normal, OC0 disconnected 01 WGM1[3:0] = 9 or 14: toggle OCnA on compare match, OCnB disconnected WGM1[3:0]= other settings, OC1A/1B disconnected 10 Clear OC0 on compare match when up-counting. Set OC0 on compare match when down counting 11 Set OC0 on compare match when up-counting. Clear OC0 on compare match when down counting. Fast PWM COMx[1:0] Description 00 Normal, OC1A/1B disconnected 01 WGM1[3:0] = 9 or 11, toggle OC1A on compare match OC1B disconnected WGM1[3:0] = other settings, OC1A/1B disconnected 10 Clear OC1A/1B on compare match, set OC1A/1B on Compare Match when down counting 11 Set OC1A/1B on compare match when upcounting. Clear OC1A/1B on Compare Match when upcounting

Figure 7.12: TCCR1A and TCCR1B registers.

7.8. TIMER 2

193

7.7.1.3 Output Compare Register 1 (OCR1AH/OCR1AL)

The OCR1A register holds a user-defined 16-bit value that is continuously compared to the TCNT1 register when Channel A is used. 7.7.1.4 OCR1BH/OCR1BL The OCR1B register holds a user-defined 16-bit value that is continuously compared to the TCNT1 register when Channel B is used. 7.7.1.5 Input Capture Register 1 (ICR1H/ICR1L)

ICR1 is a 16-bit register used to capture the value of the TCNT1 register when a desired edge on ICP1 pin has occurred. 7.7.1.6 Timer/Counter Interrupt Mask Register 1 (TIMSK1) Timer 1 uses the Timer/Counter 1 Output Compare Match Interrupt Enable (OCIE1A/1B) bits, the Timer/Counter 1 Overflow Interrupt Enable (TOIE1) bit, and the Timer/Counter 1 Input Capture Interrupt Enable (IC1E1) bit. When the OCIE1A/B bit and the I-bit in the Status Register are both set to one, the Timer/Counter 1 Compare Match interrupt is enabled. When the OIE1 bit and the I-bit in the Status Register are both set to one, the Timer/Counter 1 Overflow interrupt is enabled. When the IC1E1 bit and the I-bit in the Status Register are both set to one, the Timer/Counter 1 Input Capture interrupt is enabled. 7.7.1.7 Timer/Counter Interrupt Flag Register (TIFR1)

Timer 1 uses the Output Compare Flag 1 A/B (OCF1A/B) which sets for an output compare A/B match. Timer 1 also uses the Timer/Counter 1 Overflow Flag (TOV1) which sets when Timer/Counter 1 overflows. Timer Channel 1 also uses the Timer/Counter 1 Input Capture Flag (ICF1) which sets for an input capture event.

7.8

TIMER 2

Timer 2 is another 8-bit timer channel similar to Timer 0. The Timer 2 channel block diagram is provided in Figure 7.13. Its registers are summarized in Figure 7.14. 7.8.0.8 Timer/Counter Control Register A and B (TCCR2A and B)

The TCCR2A and B register bits are used to: • Select the operational mode of Timer 2 using the Waveform Mode Generation (WGM2[2:0]) bits, • Determine the operation of the timer within a specific mode with the Compare Match Output Mode (COM2A[1:0] and B) bits, and

194

7. TIMING SUBSYSTEM

Figure 7.13: Timer 2 block diagram. (Figure used with Permission, Atmel,Inc.)

7.8. TIMER 2

Timer/Counter Control Register A (TCCR2A) ---

COM2A1 COM2A0 COM2B1 COM2B0

---

WGM21 WGM20

7 Timer/Counter Control Register B (TCCR2B) FOC2A FOC2B

---

---

WGM22 CS22

7

0 CS21

CS20 0

Timer/Counter Register (TCNT2) 7 Output Compare Register A (OCR2A)

0

7 Output Compare Register B (OCR2B)

0

7 Timer/Counter 2 Interrupt Mask Register (TIMSK2)

0

---

---

---

---

---

OCIE2B OCIE2A TOIE2

7 Timer/Counter 2 Interrupt Flag REgister (TIFR2) ---

---

7 Figure 7.14: Timer 2 registers.

---

---

---

0

OCF2B OCF2A TOV2 0

195

196

7. TIMING SUBSYSTEM

• Select the source of the Timer 2 clock using Clock Select (CS2[2:0]) bits. The bit settings for the TCCR2A and B registers are summarized in Figure 7.15. 7.8.0.9 Timer/Counter Register(TCNT2)

The TCNT2 is the 8-bit counter for Timer 2. 7.8.0.10 Output Compare Register A and B (OCR2A and B)

The OCR2A and B registers hold a user-defined 8-bit value that is continuously compared to the TCNT2 register. 7.8.0.11 Timer/Counter Interrupt Mask Register 2 (TIMSK2) Timer 2 uses the Timer/Counter 2 Output Compare Match Interrupt Enable A and B (OCIE2A and B) bits and the Timer/Counter 2 Overflow Interrupt Enable A and B (OIE2A and B) bits. When the OCIE2A or B bit and the I-bit in the Status Register are both set to one, the Timer/Counter 2 Compare Match interrupt is enabled. When the TOIE2 bit and the I-bit in the Status Register are both set to one, the Timer/Counter 2 Overflow interrupt is enabled. 7.8.0.12 Timer/Counter Interrupt Flag Register 2 (TIFR2)

Timer 2 uses the Output Compare Flags 2 A and B (OCF2A and B) which sets for an output compare match. Timer 2 also uses the Timer/Counter 2 Overflow Flag (TOV2) which sets when Timer/Counter 2 overflows.

7.9

PROGRAMMING THE ARDUINO UNO R3 USING THE BUILT-IN ARDUINO DEVELOPMENT ENVIRONMENT TIMING FEATURES

The Arduino Development Environment has several built-in timing features. These include: • delay(unsigned long): The delay function pauses a sketch for the amount of time specified in milliseconds. • delayMicroseconds(unsigned int): The delayMicroseconds function pauses a sketch for the amount of time specified in microseconds. • pulseIn(pin, value): The pulseIn function measures the length of an incoming digital pulse. If value is specified as HIGH, the function waits for the specified pin to go high and then times until the pin goes low. The pulseIn function returns the length of elapsed time in microseconds as an unsigned long. • analogWrite(pin, value): The analog write function provides a pulse width modulated (PWM) output signal on the specified pin. The PWM frequency is approximately 490 Hz. The duty cycle is specified from 0 (value of 0) to 100 (value of 255) percent.

7.9. PROGRAMMING THE ARDUINO UNO R3 CS2[2:0] 000 001 010 011 100 101 110 111

Clock Source None clkI/0 clkI/0/8 clkI/0/32 clkI/0/64 clkI/0/128 clkI/0/256 clkI/0/1024 Clock Select


---

---

WGM22 CS22

7 Timer/Counter Control Register A (TCCR2A) COM2A1 COM2A0 COM2B1 COM2B0 ---

CS21

CS20 0

---

WGM21 WGM20

Waveform Generation Mode Mode WGM[02:00] Mode 0 000 Normal 1 001 PWM, Phase Correct 2 010 CTC 3 011 Fast PWM 4 100 Reserved 5 101 PWM, Phase Correct 6 110 Reserved 7 111 Fast PWM Compare Output Mode, non-PWM Mode COM2A[1:0] Description 00 Normal, OC2A disconnected 01 Toggle OC2A on compare match 10 Clear OC2A on compare match 11 Set OC2A on compare match

Compare Output Mode, non-PWM Mode COM2B[1:0] Description 00 Normal, OC2B disconnected 01 Toggle OC2B on compare match 10 Clear OC2B on compare match 11 Set OC2B on compare match

Compare Output Mode, Fast PWM Mode COM2A[1:0] Description 00 Normal, OC2A disconnected 01 WGM22 = 0: normal operation, OC2A disconnected WGM22 = 1: Toggle OC2A on compare match 10 Clear OC2A on compare match, set OC2A at Bottom (non-inverting mode) 11 Set OC2A on compare match, clear OC2A at Bottom (inverting mode)

Compare Output Mode, Fast PWM Mode COM2B[1:0] Description 00 Normal, OC2B disconnected 01 Reserved



COM2A[1:0] Description 00 Normal, OC2A disconnected 01 WGM22 = 0: normal operation, OC2A disconnected WGM22 = 1: Toggle OC2A on compare match Clear OC2A on compare match, 10 when upcounting. Set OC2A on compare match when down counting Set OC2A on compare match, 11 when upcounting. Set OC2A on compare match when down counting

10

11

Clear OC2B on compare match, set OC2B at Bottom (non-inverting mode) Set OC2B on compare match, clear OC2B at Bottom (inverting mode)

COM2B[1:0] Description 00 Normal, OC2B disconnected 01 Reserved

10

11

Clear OC2B on compare match, when upcounting. Set OC2B on compare match when down counting Set OC2B on compare match, when upcounting. Set OC2B on compare match when down counting

Figure 7.15: Timer/Counter Control Register A and B (TCCR2A and B) bit settings.

197

198

7. TIMING SUBSYSTEM

We have already used the analogWrite function in an earlier chapter to control the motor speed of the Blinky 602A robot.

7.10 PROGRAMMING THE TIMER SYSTEM IN C In this section, we provide several representative examples of using the timer system for various applications. We will provide examples of using the timer system to generate a prescribed delay, to generate a PWM signal, and to capture an input event.

7.10.1 PRECISION DELAY IN C In this example, we program the ATmega328 to provide a delay of some number of 6.55 ms interrupts. The Timer 0 overflow is configured to occur every 6.55 ms. The overflow flag is used as a “clock tick” to generate a precision delay. To create the delay the microcontroller is placed in a while loop waiting for the prescribed number of Timer 0 overflows to occur.

//Function prototypes void delay(unsigned int number_of_6_55ms_interrupts); void init_timer0_ovf_interrupt(void); void timer0_interrupt_isr(void);

//interrupt handler definition #pragma interrupt_handler timer0_interrupt_isr:17 //door profile data

//************************************************************************* //int_timer0_ovf_interrupt(): The Timer0 overflow interrupt is being //employed as a time base for a master timer for this project. //The ceramic resonator operating at 10 MHz is divided by 256. //The 8-bit Timer0 register (TCNT0) overflows every 256 counts //or every 6.55 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0B = 0x04; //divide timer0 timebase by 256, overfl. occurs every 6.55ms TIMSK0 = 0x01; //enable timer0 overflow interrupt

7.10. PROGRAMMING THE TIMER SYSTEM IN C

asm("SEI"); }

199

//enable global interrupt

//************************************************************************* //************************************************************************* //timer0_interrupt_isr: //Note: Timer overflow 0 is cleared by hardware when executing the //corresponding interrupt handling vector. //*************************************************************************

void timer0_interrupt_isr(void) { input_delay++; //input delay processing } //************************************************************************* //************************************************************************* //delay(unsigned int num_of_6_55ms_interrupts): this generic delay function //provides the specified delay as the number of 6.55 ms "clock ticks" from //the Timer0 interrupt. //Note: this function is only valid when using a 10 MHz crystal or ceramic // resonator //************************************************************************* void delay(unsigned int number_of_6_55ms_interrupts) { TCNT0 = 0x00; //reset timer0 input_delay = 0; while(input_delay <= number_of_6_55ms_interrupts) { ; } } //*************************************************************************

200

7. TIMING SUBSYSTEM

7.10.2 PULSE WIDTH MODULATION IN C The function provided below is used to configure output compare channel B to generate a pulse width modulated signal. An analog voltage provided to ADC Channel 3 is used to set the desired duty cycle from 50 to 100 percent. Note how the PWM ramps up from 0 to the desired speed. //Function Prototypes void PWM(unsigned int PWM_incr) { unsigned int Open_Speed_int; float Open_Speed_float; int gate_position_int;

PWM_duty_cycle = 0; InitADC();

//Initialize ADC

Open_Speed_int = ReadADC(0x03);

//Read "Open Speed" volt //setting PA3 //Open Speed Setting unsigned int //Convert to max duty cycle

//setting //0 VDC = 50% = 127, //5 VDC = 100% =255 Open_Speed_float = ((float)(Open_Speed_int)/(float)(0x0400)); //Convert volt to PWM constant //127-255 Open_Speed_int = (unsigned int)((Open_Speed_float * 127) + 128.0); //Configure PWM clock TCCR1A = 0xA1; //freq = resonator/510 = 10MHz/510

TCCR1B = 0x01; PWM_duty_cycle = 0;

//freq = 19.607 kHz //no clock source division //Initiate PWM duty cycle //variables

7.10. PROGRAMMING THE TIMER SYSTEM IN C

201

OCR1BH = 0x00; OCR1BL = (unsigned char)(PWM_duty_cycle);//Set PWM duty cycle CH B to 0% //Ramp up to Open Speed in 1.6s OCR1BL = (unsigned char)(PWM_duty_cycle);//Set PWM duty cycle CH B while (PWM_duty_cycle < Open_Speed_int) { if(PWM_duty_cycle < Open_Speed_int) //Increment duty cycle PWM_duty_cycle=PWM_duty_cycle + PWM_open_incr; //Set PWM duty cycle CH B OCR1BL = (unsigned char)(PWM_duty_cycle); } //Gate continues to open at specified upper speed (PA3) : : : //*************************************************************************

7.10.3 INPUT CAPTURE MODE IN C This example was developed by Julie Sandberg, BSEE and Kari Fuller, BSEE at the University of Wyoming as part of their senior design project. In this example, the input capture channel is being used to monitor the heart rate (typically 50-120 beats per minute) of a patient. The microcontroller is set to operate at an internal clock frequency of 1 MHz. Timer/Counter channel 1 is used in this example. //************************************************************************* //initialize_ICP_interrupt: Initialize Timer/Counter 1 for input capture //************************************************************************* void initialize_ICP_interrupt(void) { TIMSK=0x20; //Allows input capture interrupts SFIOR=0x04; //Internal pull-ups disabled TCCR1A=0x00; //No output comp or waveform //generation mode TCCR1B=0x45; //Capture on rising edge, //clock prescalar=1024

202

7. TIMING SUBSYSTEM

TCNT1H=0x00; TCNT1L=0x00; asm("SEI"); }

//Initially clear timer/counter 1 //Enable global interrupts

//************************************************************************* void Input_Capture_ISR(void) { if(first_edge==0) { ICR1L=0x00; ICR1H=0x00; TCNT1L=0x00; TCNT1H=0x00; first_edge=1; } else { ICR1L=TCNT1L; ICR1H=TCNT1H; TCNT1L=0x00; TCNT1H=0x00; first_edge=0; } heart_rate(); TIFR=0x20; asm("RETI");

//Clear ICR1 and TCNT1 on first edge

//Capture time from TCNT1

//Calculate the heart rate //Clear the input capture flag //Resets the I flag to allow //global interrupts

} //************************************************************************* void heart_rate(void) { if(first_edge==0) {

7.11. SERVO MOTOR CONTROL WITH THE PWM SYSTEM IN C

203

time_pulses_low = ICR1L; //Read 8 low bits first time_pulses_high = ((unsigned int)(ICR1H << 8)); time_pulses = time_pulses_low | time_pulses_high; if(time_pulses!=0) //1 counter increment = 1.024 ms { //Divide by 977 to get seconds/pulse HR=60/(time_pulses/977); //(secs/min)/(secs/beat) =bpm } else { HR=0; } } else { HR=0; } } //*************************************************************************

7.11 SERVO MOTOR CONTROL WITH THE PWM SYSTEM IN C A servo motor provides an angular displacement from 0 to 180 degrees. Most servo motors provide the angular displacement relative to the pulse length of repetitive pulses sent to the motor as shown in Figure 7.16. A 1 ms pulse provides an angular displacement of 0 degrees while a 2 ms pulse provides a displacement of 180 degrees. Pulse lengths in between these two extremes provide angular displacements between 0 and 180 degrees. Usually, a 20 to 30 ms low signal is provided between the active pulses. A test and interface circuit for a servo motor is provided in Figure 7.16. The PB0 and PB1 inputs of the ATmega328 provide for clockwise (CW) and counter-clockwise (CCW) rotation of the servo motor, respectively. The time base for the ATmega328 is provided by a 128 KHz external RC oscillator. Also, the external time base divide-by-eight circuit is active via a fuse setting. Pulse width modulated signals to rotate the servo motor is provided by the ATmega328. A voltage-follower op amp circuit is used as a buffer between the ATmega328 and the servo motor. The software to support the test and interface circuit is provided below.

204

7. TIMING SUBSYSTEM 128 kHz ceramic resonator

VDD

1 PUR - PC6 PC5 28 2 RXD - PD0 PC4 27 3 TXD - PD1 PC3 26 4 PD2 PC2 25 5 PD3 PC1 24 6 PD4 PCO 23 7 Vcc GND 22 Atmega328 8 GND AREF 21 9 PB6 AVCC 20 10 PB7 PB5 19 11 PD5 PB4 18 12 PD6 PB3 17 13 PD7 PB2 16 14 PB0 PB1 15

sys reset 1M 1uf

Vcc = 5.0 volts 74HC14 4.7 K

CW

470K

PB0 (2)

(1) 0.1uF

100K

VDD

3K

Vcc = 5.0 volts 74HC14 4.7 K

CCW

470K

PB1 (4)

(3) 0.1uF

100K 3K

White

Vcc = 5 VDC Red Black CCW

Vcc = 5 VDC (4) (3) (1) (2) LM324 (11)

=8

% .25 o= o =3 0 180 = = s s 1m 2m

2 ms

5% 6.2

CW

6 =1

30 ms T = 32 ms, f = 31.25 Hz

Figure 7.16: Test and interface circuit for a servo motor.


205

//************************************************************************* //target controller: ATMEL ATmega328 // //ATMEL AVR ATmega328PV Controller Pin Assignments //Chip Port Function I/O Source/Dest Asserted Notes //Pin 1 PUR Reset - 1M resistor to Vdd, tact switch to ground, // 1.0 uF to ground //Pin 7 Vdd - 1.0 uF to ground //Pin 8 Gnd //Pin 9 PB6 ceramic resonator connection //Pin 10 PB7 ceramic resonator connection //PORTB: //Pin 14 PB0 to active high RC debounced switch - CW //Pin 15 PB1 to active high RC debounced switch - CCW //Pin 16 PB2 - to servo control input //Pin 20 AVcc to Vdd //Pin 21 ARef to Vdd //Pin 22 AGnd to Ground //************************************************************************* //include files************************************************************ //ATMEL register definitions for ATmega328 #include #include //function prototypes****************************************************** void initialize_ports(void); //initializes ports void read_new_input(void); //used to read input change on PORTB void init_timer0_ovf_interrupt(void); //used to initialize timer0 overflow //main program************************************************************* //The main program checks PORTB for user input activity. //If new activity is found, the program responds. //global unsigned unsigned unsigned

variables char old_PORTB = 0x08; char new_PORTB; int PWM_duty_cycle;

//present value of PORTB //new values of PORTB

206

7. TIMING SUBSYSTEM

void main(void) { initialize_ports(); //return LED configuration to default

//external ceramic resonator: 128 KHZ //fuse set for divide by 8 //configure PWM clock TCCR1A = 0xA1; //freq = oscillator/510 = 128KHz/8/510 //freq = 31.4 Hz TCCR1B = 0x01; //no clock source division //duty cycle will vary from 3.1% = //1 ms = 0 degrees = 8 counts to //6.2% = 2 ms = 180 degrees = 16 counts //initiate PWM duty cycle variables PWM_duty_cycle = 12; OCR1BH = 0x00; OCR1BL = (unsigned char)(PWM_duty_cycle); //main activity loop - processor will continually cycle through //loop for new activity. //Activity initialized by external signals presented to PORTB[1:0] while(1) { _StackCheck(); read_new_input(); } }//end main

//check for stack overflow //read input status changes on PORTB

//Function definitions //************************************************************************* //initialize_ports: provides initial configuration for I/O ports


207

//************************************************************************* void initialize_ports(void) { //PORTB DDRB=0xfc; PORTB=0x00;

//PORTB[7-2] output, PORTB[1:0] input //disable PORTB pull-up resistors


//set PORTC[7-0] as output //init low



//************************************************************************* //************************************************************************* //read_new_input: functions polls PORTB for a change in status. If status //change has occurred, appropriate function for status change is called //Pin 1 PB0 to active high RC debounced switch - CW //Pin 2 PB1 to active high RC debounced switch - CCW //************************************************************************* void read_new_input(void) { new_PORTB = (PINB); if(new_PORTB != old_PORTB){ switch(new_PORTB){ //process change in PORTB input case 0x01: //CW while(PINB == 0x01) { PWM_duty_cycle = PWM_duty_cycle + 1; if(PWM_duty_cycle > 16) PWM_duty_cycle = 16; OCR1BH = 0x00; OCR1BL = (unsigned char)(PWM_duty_cycle); }

208

7. TIMING SUBSYSTEM

break; case 0x02: //CCW while(PINB == 0x02) { PWM_duty_cycle = PWM_duty_cycle - 1; if(PWM_duty_cycle < 8) PWM_duty_cycle = 8; OCR1BH = 0x00; OCR1BL = (unsigned char)(PWM_duty_cycle); } break;

default:; } } old_PORTB=new_PORTB;

//all other cases //end switch(new_PORTB) //end if new_PORTB //update PORTB

} //*************************************************************************

7.12 SUMMARY In this chapter, we considered a microcontroller timer system, associated terminology for timer related topics, discussed typical functions of a timer subsystem, studied timer hardware operations, and considered some applications where the timer subsystem of a microcontroller can be used. We then took a detailed look at the timer subsystem aboard the ATmega328 and reviewed the features, operation, registers, and programming of the three timer channels. We then investigated the builtin timing features of the Arduino Development Environment. We concluded with an example employing a servo motor controlled by the ATmega328 PWM system.

7.13 REFERENCES • Kenneth Short, Embedded Microprocessor Systems Design: An Introduction Using the INTEL 80C188EB, Prentice Hall, Upper Saddle River, 1998. • Frederick Driscoll, Robert Coughlin, and Robert Villanucci, Data Acquisition and Process Control with the M68HC11 Microcontroller, Second Edition, Prentice Hall, Upper Saddle River, 2000.


209

• Todd Morton, Embedded Microcontrollers, Prentice Hall, Upper Saddle River, Prentice Hall, 2001. • Atmel 8-bit AVR Microcontroller with 16K Bytes In-System Programmable Flash, ATmega328, ATmega328L, data sheet: 2466L-AVR-06/05, Atmel Corporation, 2325 Orchard Parkway, San Jose, CA 95131. • Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025

7.14 CHAPTER PROBLEMS 1. Given an 8 bit free running counter and the system clock rate of 24 MHz, find the time required for the counter to count from zero to its maximum value. 2. If we desire to generate periodic signals with periods ranging from 125 nanoseconds to 500 microseconds, what is the minimum frequency of the system clock? 3. Describe how you can compute the period of an incoming signal with varying duty cycles. 4. Describe how one can generate an aperiodic pulse with a pulse width of 2 minutes? 5. Program the output compare system of the ATmega328 to generate a 1 kHz signal with a 10 percent duty cycle. 6. Design a microcontroller system to control a sprinkler controller that performs the following tasks. We assume that your microcontroller runs with 10 MHz clock and it has a 16 bit free running counter. The sprinkler controller system controls two different zones by turning sprinklers within each zone on and off. To turn on the sprinklers of a zone, the controller needs to receive a 152.589 Hz PWM signal from your microcontroller. To turn off the sprinklers of the same zone, the controller needs to receive the PWM signal with a different duty cycle. (a) Your microcontroller needs to provide the PWM signal with 10% duty cycle for 10 millisecond to turn on the sprinklers in zone one. (b) After 15 minutes, your microcontroller must send the PWM signal with 15% duty cycle for 10 millisecond to turn off the sprinklers in zone one. (c) After 15 minutes, your microcontroller must send the PWM signal with 20% duty cycle for 10 millisecond to turn on the sprinklers in zone two.

210

7. TIMING SUBSYSTEM

(d) After 15 minutes, your microcontroller must send the PWM signal with 25% duty cycle for 10 millisecond to turn off the sprinklers in zone two. 7. Modify the servo motor example to include a potentiometer connected to PORTA[0]. The servo will deflect 0 degrees for 0 VDC applied to PORTA[0] and 180 degrees for 5 VDC. 8. For the automated cooling fan example, what would be the effect of changing the PWM frequency applied to the fan? 9. Modify the code of the automated cooling fan example to also display the set threshold temperature.

211

CHAPTER

8

Atmel AVR Operating Parameters and Interfacing Objectives: After reading this chapter, the reader should be able to • Describe the voltage and current parameters for the Arduino UNO R3 and the Atmel AVR HC CMOS type microcontroller. • Specify a battery system to power an Arduino UNO R3 and the Atmel AVR based system. • Apply the voltage and current parameters toward properly interfacing input and output devices to the Arduino UNO R3 and the Atmel AVR microcontroller. • Interface a wide variety of input and output devices to the Arduino UNO R3 and the Atmel AVR microcontroller. • Describe the special concerns that must be followed when the Arduino UNO R3 and the Atmel AVR microcontroller is used to interface to a high power DC or AC device. • Discuss the requirement for an optical based interface. • Describe how to control the speed and direction of a DC motor. • Describe how to control several types of AC loads.

8.1

OVERVIEW

The textbook for Morgan & Claypool Publishers (M&C) titled, “Microcontrollers Fundamentals for Engineers and Scientists,” contains a chapter entitled “Operating Parameters and Interfacing.” With M&C permission, we repeated portions of the chapter here for your convenience. However, we have customized the information provided to the Arduino UNO R3 and the Atmel AVR line of microcontrollers and have also expanded the coverage of the chapter to include interface techniques for a number of additional input and output devices. In this chapter, we introduce you to the extremely important concepts of the operating envelope for a microcontroller. We begin by reviewing the voltage and current electrical parameters for the HC CMOS based Atmel AVR line of microcontrollers. We then show how to apply this information to properly interface input and output devices to the Arduino UNO R3 and the ATmega328

212

8. ATMEL AVR OPERATING PARAMETERS AND INTERFACING

microcontroller. We then discuss the special considerations for controlling a high power DC or AC load such as a motor and introduce the concept of an optical interface. Throughout the chapter, we provide a number of detailed examples. The importance of this chapter can not be emphasized enough. Any time an input or an output device is connected to a microcontroller, the interface between the device and the microcontroller must be carefully analyzed and designed.This will ensure the microcontroller will continue to operate within specified parameters. Should the microcontroller be operated outside its operational envelope, erratic, unpredictable, and unreliable system may result.

8.2

OPERATING PARAMETERS

Any time a device is connected to a microcontroller, careful interface analysis must be performed. Most microcontrollers are members of the “HC,” or high-speed CMOS, family of chips. As long as all components in a system are also of the “HC” family, as is the case for the Arduino UNO R3 and the Atmel AVR line of microcontrollers, electrical interface issues are minimal. If the microcontroller is connected to some component not in the “HC” family, electrical interface analysis must be completed. Manufacturers readily provide the electrical characteristic data necessary to complete this analysis in their support documentation. To perform the interface analysis, there are eight different electrical specifications required for electrical interface analysis. The electrical parameters are: • VOH : the lowest guaranteed output voltage for a logic high, • VOL : the highest guaranteed output voltage for a logic low, • IOH : the output current for a VOH logic high, • IOL : the output current for a VOL logic low, • VI H : the lowest input voltage guaranteed to be recognized as a logic high, • VI L : the highest input voltage guaranteed to be recognized as a logic low, • II H : the input current for a VI H logic high, and • II L : the input current for a VI L logic low. These electrical characteristics are required for both the microcontroller and the external components. Typical values for a microcontroller in the HC CMOS family assuming VDD = 5.0 volts and VSS = 0 volts are provided below. The minus sign on several of the currents indicates a current flow out of the device. A positive current indicates current flow into the device. • VOH = 4.2 volts, • VOL = 0.4 volts,

8.2. OPERATING PARAMETERS

213

• IOH = -0.8 milliamps, • IOL = 1.6 milliamps, • VI H = 3.5 volts, • VI L = 1.0 volt, • II H = 10 microamps, and • II L = -10 microamps. It is important to realize that these are static values taken under very specific operating conditions. If external circuitry is connected such that the microcontroller acts as a current source (current leaving the microcontroller) or current sink (current entering the microcontroller), the voltage parameters listed above will also be affected. In the current source case, an output voltage VOH is provided at the output pin of the microcontroller when the load connected to this pin draws a current of IOH . If a load draws more current from the output pin than the IOH specification, the value of VOH is reduced. If the load current becomes too high, the value of VOH falls below the value of VI H for the subsequent logic circuit stage and not be recognized as an acceptable logic high signal. When this situation occurs, erratic and unpredictable circuit behavior results. In the sink case, an output voltage VOL is provided at the output pin of the microcontroller when the load connected to this pin delivers a current of IOL to this logic pin. If a load delivers more current to the output pin of the microcontroller than the IOL specification, the value of VOL increases. If the load current becomes too high, the value of VOL rises above the value of VI L for the subsequent logic circuit stage and not be recognized as an acceptable logic low signal. As before, when this situation occurs, erratic and unpredictable circuit behavior results. For convenience this information is illustrated in Figure 8.1. In (a), we provided an illustration of the direction of current flow from the HC device and also a comparison of voltage levels. As a reminder current flowing out of a device is considered a negative current (source case) while current flowing into the device is considered positive current(sink case). The magnitude of the voltage and current for HC CMOS devices are shown in (b). As more current is sinked or sourced from a microcontroller pin, the voltage will be pulled up or pulled down, respectively, as shown in (c). If input and output devices are improperly interfaced to the microcontroller, these loading conditions may become excessive, and voltages will not be properly interpreted as the correct logic levels. You must also ensure that total current limits for an entire microcontroller port and overall bulk port specifications are complied with. For planning purposes the sum of current sourced or sinked from a port should not exceed 100 mA. Furthermore, the sum of currents for all ports should not exceed 200 mA. As before, if these guidelines are not followed, erratic microcontroller behavior may result. The procedures presented in the following sections, when followed carefully, will ensure the microcontroller will operate within its designed envelope.The remainder of the chapter is divided into

214


Input Gate Parameters VDD = 5 VDC

Output Gate Parameters VDD = 5 VDC VOH

IOH

VOL

IOL

IIH

VIH

IIL

VIL VSS = 0 VDC

VSS = 0 VDC

a) Voltage and current electrical parameters Output Parameters

Input Parameters

VOH = 4.2 V

VIH = 3.5 V

VOL = 0.4 V

VIL = 1.0 V

IOH = - 0.8 mA

IIH = 10 μA

IOL = 1.6 mA

IIL = - 10 μA

b) HC CMOS voltage and current parameters Current sink

0

Current source

Iout [mA]

-25

Iout [mA]

25

0

Vout [V]

5

0

5

Vout [V]

c) CMOS loading curves

Figure 8.1: Electrical voltage and current parameters.

0

8.3. BATTERY OPERATION

215

input device interface analysis followed by output device interface analysis. Since many embedded systems operate from a DC battery source, we begin by examining several basic battery supply circuits.

8.3

BATTERY OPERATION

Many embedded systems are remote, portable systems operating from a battery supply. To properly design a battery source for an embedded system, the operating characteristics of the embedded system must be matched to the characteristics of the battery supply.

8.3.1

EMBEDDED SYSTEM VOLTAGE AND CURRENT DRAIN SPECIFICATIONS

An embedded system has a required supply voltage and an overall current requirement. For the purposes of illustration, we will assume our microcontroller based embedded system operates from 5 VDC. The overall current requirements of the system is determined by the worst case current requirements when all embedded system components are operational.

8.3.2

BATTERY CHARACTERISTICS

To properly match a battery to an embedded system, the battery voltage and capacity must be specified. Battery capacity is typically specified as a mAH rating. For example, a typical 9 VDC nonrechargeable alkaline battery has a capacity of 550 mAH. If the embedded system has a maximum operating current of 50 mA, it will operate for approximately eleven hours before battery replacement is required. A battery is typically used with a voltage regulator to maintain the voltage at a prescribed level. Figure 8.2 provides sample circuits to provide a +5 VDC and a ±5 VDC portable battery source. Additional information on battery capacity and characteristics may be found in Barrett and Pack [Prentice-Hall, 2005].

8.4

INPUT DEVICES

In this section, we discuss how to properly interface input devices to a microcontroller. We will start with the most basic input component, a simple on/off switch.

8.4.1

SWITCHES

Switches come in a variety of types. As a system designer it is up to you to choose the appropriate switch for a specific application. Switch varieties commonly used in microcontroller applications are illustrated in Figure 8.3(a). Here is a brief summary of the different types: • Slide switch: A slide switch has two different positions: on and off. The switch is manually moved to one position or the other. For microcontroller applications, slide switches are available

216


I

7805

O

+5 VDC

C 9 VDC

0.33 uF

0.1 uF

a) +5 VDC battery supply.

I

7805

O

+5 VDC

C 9 VDC

0.33 uF

0.1 uF

9 VDC

0.33 uF

0.1 uF

C I

7905

O

-5 VDC

b) +/-5 VDC battery supply.

Figure 8.2: Battery supply circuits employing a 9 VDC battery with a 5 VDC regulators.

8.4. INPUT DEVICES

217

that fit in the profile of a common integrated circuit size dual inline package (DIP). A bank of four or eight DIP switches in a single package is commonly available. • Momentary contact pushbutton switch: A momentary contact pushbutton switch comes in two varieties: normally closed (NC) and normally open (NO). A normally open switch, as its name implies, does not normally provide an electrical connection between its contacts. When the pushbutton portion of the switch is depressed, the connection between the two switch contacts is made. The connection is held as long as the switch is depressed. When the switch is released the connection is opened. The converse is true for a normally closed switch. For microcontroller applications, pushbutton switches are available in a small tact type switch configuration. • Push on/push off switches: These type of switches are also available in a normally open or normally closed configuration. For the normally open configuration, the switch is depressed to make connection between the two switch contacts. The pushbutton must be depressed again to release the connection. • Hexadecimal rotary switches: Small profile rotary switches are available for microcontroller applications. These switches commonly have sixteen rotary switch positions. As the switch is rotated to each position, a unique four bit binary code is provided at the switch contacts. A common switch interface is shown in Figure 8.3(b). This interface allows a logic one or zero to be properly introduced to a microcontroller input port pin.The basic interface consists of the switch in series with a current limiting resistor. The node between the switch and the resistor is provided to the microcontroller input pin. In the configuration shown, the resistor pulls the microcontroller input up to the supply voltage VDD . When the switch is closed, the node is grounded and a logic zero is provided to the microcontroller input pin. To reverse the logic of the switch configuration, the position of the resistor and the switch is simply reversed.

8.4.2

PULLUP RESISTORS IN SWITCH INTERFACE CIRCUITRY

Many microcontrollers are equipped with pullup resistors at the input pins. The pullup resistors are asserted with the appropriate register setting. The pullup resistor replaces the external resistor in the switch configuration as shown in Figure 8.3b) right.

8.4.3

SWITCH DEBOUNCING

Mechanical switches do not make a clean transition from one position (on) to another (off ). When a switch is moved from one position to another, it makes and breaks contact multiple times. This activity may go on for tens of milliseconds. A microcontroller is relatively fast as compared to the action of the switch. Therefore, the microcontroller is able to recognize each switch bounce as a separate and erroneous transition.

218


0

DIP switch

Tact switch

PB switch

Hexadecimal rotary switch

a) Switch varieties VDD

VDD

4.7 kohm To microcontroller input - Logic one when switch open - Logic zero when switch is closed

b) Switch interface VDD 4.7 k ohm

74HC14

470 k ohm

0.1 μF

c) Switch interface equipped with debouncing circuitry

Figure 8.3: Switch interface.

microcontroller pullup resistor activated

8.4. INPUT DEVICES

219

To correct the switch bounce phenomena additional external hardware components may be used or software techniques may be employed. A hardware debounce circuit is illustrated in Figure 8.3(c). The node between the switch and the limiting resistor of the basic switch circuit is fed to a low pass filter (LPF) formed by the 470 k ohm resistor and the capacitor. The LPF prevents abrupt changes (bounces) in the input signal from the microcontroller. The LPF is followed by a 74HC14 Schmitt Trigger, which is simply an inverter equipped with hysteresis. This further limits the switch bouncing. Switches may also be debounced using software techniques. This is accomplished by inserting a 30 to 50 ms lockout delay in the function responding to port pin changes. The delay prevents the microcontroller from responding to the multiple switch transitions related to bouncing. You must carefully analyze a given design to determine if hardware or software switch debouncing techniques will be used. It is important to remember that all switches exhibit bounce phenomena and, therefore, must be debounced.

8.4.4

KEYPADS

A keypad is simply an extension of the simple switch configuration. A typical keypad configuration and interface are shown in Figure 8.4. As you can see the keypad is simply multiple switches in the same package. A hexadecimal keypad is provided in the figure. A single row of keypad switches are asserted by the microcontroller and then the host keypad port is immediately read. If a switch has been depressed, the keypad pin corresponding to the column the switch is in will also be asserted. The combination of a row and a column assertion can be decoded to determine which key has been pressed as illustrated in the table. Keypad rows are continually asserted one after the other in sequence. Since the keypad is a collection of switches, debounce techniques must also be employed. The keypad may be used to introduce user requests to a microcontroller. A standard keypad with alphanumeric characters may be used to provide alphanumeric values to the microcontroller such as providing your personal identification number (PIN) for a financial transaction. However, some keypads are equipped with removable switch covers such that any activity can be associated with a key press. In Figure 8.5, we have connected the ATmega328 to a hexadecimal keypad via PORTB. PORTB[3:0] is configured as output to selectively assert each row. PORTB[7:4] is configured as input. Each row is sequentially asserted low. Each column is then read via PORTB[7:4] to see if any switch in that row has been depressed. If no switches have been depressed in the row, an “F” will be read from PORTB[7:4]. If a switch has been depressed, some other value than “F” will be read. The read value is then passed into a switch statement to determine the ASCII equivalent of the depressed switch. The function is not exited until the switch is released. This prevents a switch “double hit.” //*************************************************************************

8. ATMEL AVR OPERATING PARAMETERS AND INTERFACING 0

1

4

5

8

3

6

9

C

4

2

1

assert keypad row 1

2

assert keypad row 2

3

assert keypad row 3

PORTx[0]

PORTx[1]

B

E

5

assert keypad row 0

7

A

D

0

PORTx[2]

F

6

PORTx[3]

Vcc

7

10K read keypad column 0

PORTx[4] Vcc 10K

read keypad column 1

PORTx[5] Vcc 10K


PORTx[6] Vcc 10K


Key pressed by user 0 1 2 3 4 5 6 7 8 9 A B C D E F none

Figure 8.4: Keypad interface.

PORTx[7]

Row asserted Column response Row/Column by from combination microcontroller keypad switch read at micro port 3 2 1 0 7 6 5 4 1 1 1 1 1 1 1 1 1 1 1 1 0 0 0 0 X

1 1 1 1 1 1 1 1 0 0 0 0 1 1 1 1 X

1 1 1 1 0 0 0 0 1 1 1 1 1 1 1 1 X

0 0 0 0 1 1 1 1 1 1 1 1 1 1 1 1 X

1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1

1 1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1

1 0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1

0 1 1 1 0 1 1 1 0 1 1 1 0 1 1 1 1

0xEE 0xDE 0xBE 0x7E 0xED 0xDD 0xBD 0x7D 0xEB 0xDB 0xBB 0x7B 0xE7 0xD7 0xB7 0x77 0xXF

Microcontroller PORTx

220

8.4. INPUT DEVICES

Atmega328

VDD

1M


sys reset 1.0 uF


Vcc

Vcc

Vcc

Vcc

10K

10K

10K

10K

PB4

PB5

PB6

4

5

6

0

1

VDD

PB7 7 2

3

PB0 0 4

5

6

7

PB1 1 8

9

A

B

PB2 2 C

D

E

F

PB3 3

Figure 8.5: Hexadecimal keypad interface to microcontroller.

221

222


unsigned char get_keypad_value(void) { unsigned char PORTB_value, PORTB_value_masked; unsigned char ascii_value; DDRC = 0x0F; //set PORTB[7:4] to input, //PORTB[3:0] to output

PORTB = 0xFE; PORTB_value = PINB; PORTB_value_masked = (PORTB_value & 0xf0);

//switch depressed in row 0? //assert row 0 via PORTB[0] //read PORTB //mask PORTB[3:0] //switch depressed in row 1?

if(PORTB_value_masked == 0xf0) //no switches depressed in row 0 { PORTB = 0xFD; //assert Row 1 via PORTB[1] PORTB_value = PINB; //read PORTB PORTB_value_masked = (PORTB_value & 0xf0);//mask PORTB[3:0] } //switch depressed in row 2? if(PORTB_value_masked == 0xf0) //no switches depressed in row 0 { PORTB = 0xFB; //assert Row 2 via PORTC[2] PORTB_value = PINB; //read PORTB PORTB_value_masked = (PORTB_value & 0xf0);//mask PORTB[3:0] } //switch depressed in row 3? if(PORTB_value_masked == 0xf0) //no switches depressed in row 0 { PORTB = 0xF7; //assert Row 3 via PORTB[3] PORTB_value = PINB; //read PORTB PORTB_value_masked = (PORTB_value & 0xf0);//mask PORTB[3:0]

8.4. INPUT DEVICES

} if(PORTB_value_masked != 0xf0) { switch(PORTB_value_masked) { case 0xEE: ascii_value = ’0’; break; case 0xDE: ascii_value = ’1’; break; case 0xBE: ascii_value = ’2’; break; case 0x7E: ascii_value = ’3’; break; case 0xED: ascii_value = ’4’; break; case 0xDD: ascii_value = ’5’; break; case 0xBD: ascii_value = ’6’; break; case 0x7D: ascii_value = ’7’; break; case 0xEB: ascii_value = ’8’; break; case 0xDB: ascii_value = ’9’; break; case 0xBB: ascii_value = ’a’; break;

223

224


case 0x&B: ascii_value = ’b’; break; case 0xE7: ascii_value = ’c’; break; case 0xD7: ascii_value = ’d’; break; case 0xB7: ascii_value = ’e’; break; case 0x77: ascii_value = ’f’; break; default:; } while(PORTB_value_masked != 0xf0); //wait for key to be released return ascii_value; } //*************************************************************************

8.4.5

SENSORS

A microcontroller is typically used in control applications where data is collected, the data is assimilated and processed by the host algorithm, and a control decision and accompanying signals are provided by the microcontroller. Input data for the microcontroller is collected by a complement of input sensors. These sensors may be digital or analog in nature. 8.4.5.1 Digital Sensors

Digital sensors provide a series of digital logic pulses with sensor data encoded. The sensor data may be encoded in any of the parameters associated with the digital pulse train such as duty cycle, frequency, period, or pulse rate.The input portion of the timing system may be configured to measure these parameters. An example of a digital sensor is the optical encoder. An optical encoder consists of a small plastic transparent disk with opaque lines etched into the disk surface. A stationary optical emitter

8.4. INPUT DEVICES

225

and detector pair is placed on either side of the disk. As the disk rotates, the opaque lines break the continuity between the optical source and detector. The signal from the optical detector is monitored to determine disk rotation as shown in Figure 8.6.

stationary optical source and detector pair D

rotating disk S

Detector output

a) Incremental tachometer encoder

Ch A Ch B

b) Incremental quadrature encoder

Figure 8.6: Optical encoder.

Optical encoders are available in a variety of types depending on the information desired. There are two major types of optical encoders: incremental encoders and absolute encoders. An absolute encoder is used when it is required to retain position information when power is lost. For example, if you were using an optical encoder in a security gate control system, an absolute encoder would be used to monitor the gate position. An incremental encoder is used in applications where a velocity or a velocity and direction information is required. The incremental encoder types may be further subdivided into tachometers and quadrature encoders. An incremental tachometer encoder consists of a single track of etched opaque lines as shown in Figure 8.6(a). It is used when the velocity of a rotating device is required. To calculate

226


velocity, the number of detector pulses are counted in a fixed amount of time. Since the number of pulses per encoder revolution is known, velocity may be calculated. The quadrature encoder contains two tracks shifted in relationship to one another by 90 degrees. This allows the calculation of both velocity and direction. To determine direction, one would monitor the phase relationship between Channel A and Channel B as shown in Figure 8.6(b). The absolute encoder is equipped with multiple data tracks to determine the precise location of the encoder disk [Sick Stegmann]. 8.4.5.2 Analog Sensors

Analog sensors provide a DC voltage that is proportional to the physical parameter being measured. As discussed in the analog to digital conversion chapter, the analog signal may be first preprocessed by external analog hardware such that it falls within the voltage references of the conversion subsystem. The analog voltage is then converted to a corresponding binary representation. An example of an analog sensor is the flex sensor shown in Figure 8.7(a). The flex sensor provides a change in resistance for a change in sensor flexure. At 0 degrees flex, the sensor provides 10k ohms of resistance. For 90 degrees flex, the sensor provides 30-40k ohms of resistance. Since the microcontroller can not measure resistance directly, the change in flex sensor resistance must be converted to a change in a DC voltage.This is accomplished using the voltage divider network shown in Figure 8.7(c). For increased flex, the DC voltage will increase. The voltage can be measured using the ATmega328’s analog to digital converter subsystem. The flex sensor may be used in applications such as virtual reality data gloves, robotic sensors, biometric sensors, and in science and engineering experiments [Images Company].

8.4.6

LM34 TEMPERATURE SENSOR EXAMPLE

Temperature may be sensed using an LM34 (Fahrenheit) or LM35 (Centigrade) temperature transducer. The LM34 provides an output voltage that is linearly related to temperature. For example, the LM34D operates from 32 degrees F to 212 degrees F providing +10mV/degree Fahrenheit resolution with a typical accuracy of ±0.5 degrees Fahrenheit [National]. This sensor is used in the automated cooling fan example at the end of the chapter. The output from the sensor is typically connected to the ADC input of the microcontroller.

8.5

OUTPUT DEVICES

As previously mentioned, an external device should not be connected to a microcontroller without first performing careful interface analysis to ensure the voltage, current, and timing requirements of the microcontroller and the external device. In this section, we describe interface considerations for a wide variety of external devices. We begin with the interface for a single light emitting diode.

8.5. OUTPUT DEVICES

227

0.25 in (0.635 cm)

4.5 in (11.43 cm) a) flex sensor physical dimensions VDD = 5 VDC 10K fixed resistor

b) flex action

flex sensor: -- 0 degree flex, 10K -- 90 degree flex, 30-40K

c) equivalent circuit

Figure 8.7: Flex sensor.

8.5.1

LIGHT EMITTING DIODES (LEDS)

An LED is typically used as a logic indicator to inform the presence of a logic one or a logic zero at a specific pin of a microcontroller. An LED has two leads: the anode or positive lead and the cathode or negative lead. To properly bias an LED, the anode lead must be biased at a level approximately 1.7 to 2.2 volts higher than the cathode lead. This specification is known as the forward voltage (Vf ) of the LED. The LED current must also be limited to a safe level known as the forward current (If ). The diode voltage and current specifications are usually provided by the manufacturer. An example of an LED biasing circuit is provided in Figure 8.8. A logic one is provided by the microcontroller to the input of the inverter. The inverter provides a logic zero at its output which provides a virtual ground at the cathode of the LED. Therefore, the proper voltage biasing for the LED is provided. The resistor (R) limits the current through the LED. A proper resistor value can be calculated using R = (VDD − VDI ODE )/IDI ODE . It is important to note that a 7404 inverter must be used due to its capability to safely sink 16 mA of current. Alternately, an NPN transistor

228


such as a 2N2222 (PN2222 or MPQ2222) may be used in place of the inverter as shown in the figure. In Chapter 1, we used large (10 mm) red LEDs in the KNH instrumentation project. These LEDs have Vf of 6 to 12 VDC and If of 20 mA at 1.85 VDC. This requires the interface circuit shown in Figure 8.8c) right.

Vcc = 5 VDC

Vcc = 5 VDC

I

I

R2

R

+

+

from micro

Vcc = 9 VDC

I

from micro

7404

220 +

from micro

4.7K

R1

Figure 8.8: LED display devices.

8.5.2

SEVEN SEGMENT LED DISPLAYS

To display numeric data, seven segment LED displays are available as shown in Figure 8.9(a). Different numerals can be displayed by asserting the proper LED segments. For example, to display the number five, segments a, c, d, f, and g would be illuminated. Seven segment displays are available in common cathode (CC) and common anode (CA) configurations. As the CC designation implies, all seven individual LED cathodes on the display are tied together. The microcontroller is not capable of driving the LED segments directly. As shown in Figure 8.9(a), an interface circuit is required. We use a 74LS244 octal buffer/driver circuit to boost the current available for the LED. The LS244 is capable of providing 15 mA per segment (IOH ) at 2.0 VDC (VOH ). A limiting resistor is required for each segment to limit the current to a safe value for the LED. Conveniently, resistors are available in DIP packages of eight for this type of application. Seven segment displays are available in multi-character panels. In this case, separate microcontroller ports are not used to provide data to each seven segment character. Instead, a single port is used to provide character data. A portion of another port is used to sequence through each of the characters as shown in Figure 8.9(b). An NPN (for a CC display) transistor is connected to the common cathode connection of each individual character. As the base contact of each transistor is sequentially asserted, the specific character is illuminated. If the microcontroller sequences through the display characters at a rate greater than 30 Hz, the display will have steady illumination.

8.5. OUTPUT DEVICES

VOH: 2.0 VDC IOH : 15 mA

microcontroller port

a b c d e f g

common cathode 7-segment display (Vf 1.85 VDC @ If 12mA)

DIP resistor

a f

74LS244 octal buffer/ line driver

b g

e

c

R = (VOH - Vf) / If R = (2.0 - 1.85)/ 12 mA R = 12.5 ohms a) seven segment display interface

74LS244 octal buffer/ line driver

quad common cathode 7-segment display

5 VDC (20)

PORTC[7]

PORTC[0]

dp a b c d e f g

(18)

(1)

(16)

(dp)3

(16)

(2)

(15)

(a)11

(14)

(3)

(14)

(b) 7

(12)

(4)

(13)

(c) 4

(9)

(5)

(12)

(d) 2

(7)

(6)

(11)

(e) 1

(5)

(7)

(10)

(f) 10

(3) (10)

(1)

(19)

/1G

/2G

d

(8)

(9)

a f

e

(g) 5

numeral select PORTD[0]

a

f

g

10K

PORTD[3]

a b

f

b

g c

a

f

b

b

g

e

c

g

e

c

e

c

d

d

d

d

(6)

(8)

(9)

(12)

(1)

(7)

(8)

(14)

(10)

(12)

(2)

10K

(6)

10K

(9)

10K

(13)

MPQ2222

(3)

(5)

a PORTC[6]

b PORTC[5]

c PORTC[4]

d PORTC[3]

e PORTC[2]

f PORTC[1]

g PORTC[0]

hex rep

0 1 2 3 4 5 6 7 8 9

dp PORTC[7]

numeral

b) quad seven segment display interface

1 0 1 1 0 1 0 1 1 1

1 1 1 1 1 0 0 1 1 1

1 1 0 1 1 1 1 1 1 1

1 0 1 1 0 1 1 0 1 0

1 0 1 0 0 0 1 0 1 0

1 0 0 0 1 1 1 0 1 1

0 0 1 1 1 1 1 0 1 1

0x7E 0x30 0x6D 0x79 0x33 0x5D 0x1F 0x70 0x7F 0x73

c) numeral to segment converion

Figure 8.9: Seven segment LED display devices.

12 a f

b

f

g e

a b

f

e

c d

a b

f

g

g c

d

7

a

e

b g

c

e

d

6 1 d) quad seven segment display pinout UN(M)5624-11 EWRS

c d

229

230


8.5.3

CODE EXAMPLE

Provided below is a function used to illuminate the correct segments on a multi-numeral seven display. The numeral is passed in as an argument to the function along with the numerals position on the display and also an argument specifying whether or not the decimal point (dp) should be displayed at that position. The information to illuminate specific segments are provided in Figure 8.9c). //************************************************************************* void LED_character_display(unsigned int numeral, unsigned int position, unsigned int decimal_point) { unsigned char output_value; //illuminate numerical segments switch(numeral) { case 0: output_value = 0x7E; break; case 1: output_value = 0x30; break; case 2: output_value = 0x6D; break; case 3: output_value = 0x79; break; case 4: output_value = 0x33; break; case 5: output_value = 0x5D; break; case 6: output_value = 0x1F; break; case 7: output_value = 0x70; break;

8.5. OUTPUT DEVICES

231

case 8: output_value = 0x7F; break; case 9: output_value = 0x73; break; default:; } if(decimal_point != 0) PORTB = output_value | 0x80; switch(position) { case 0: PORTD = 0x01; break;

//illuminate decimal point //assert position //least significant bit

case 1: PORTD = 0x02; break;

//least significant bit + 1


//least significant bit + 2


//most significant bit

default:; } } //*************************************************************************

8.5.4

TRI-STATE LED INDICATOR

The tri-state LED indicator is shown in Figure 8.10. It is used to provide the status of an entire microcontroller port. The indicator bank consists of eight green and eight red LEDs. When an individual port pin is logic high, the green LED is illuminated. When logic low, the red LED is illuminated. If the port pin is at a tri-state high impedance state, no LED is illuminated. The NPN/PNP transistor pair at the bottom of the figure provides a 2.5 VDC voltage reference for the LEDs. When a specific port pin is logic high (5.0 VDC), the green LED will be forward biased since its anode will be at a higher potential than its cathode. The 47 ohm resistor limits

232


47

G R

47

G R

47

G

microcontroller port

R

47

G R

47

G R

47

G R

47

G R

47

G R

VDD

VDD 3.0 K

2N2222

+ LM324

3.0 K

Figure 8.10: Tri-state LED display.

2N2907

8.5. OUTPUT DEVICES

233

current to a safe value for the LED. Conversely, when a specific port pin is at a logic low (0 VDC) the red LED will be forward biased and illuminate. For clarity, the red and green LEDs are shown as being separate devices. LEDs are available that have both LEDs in the same device.

8.5.5

DOT MATRIX DISPLAY

The dot matrix display consists of a large number of LEDs configured in a single package. A typical 5 x 7 LED arrangement is a matrix of five columns of LEDs with seven LEDs per row as shown in Figure 8.11. Display data for a single matrix column [R6-R0] is provided by the microcontroller. That specific row is then asserted by the microcontroller using the column select lines [C2-C0]. The entire display is sequentially built up a column at a time. If the microcontroller sequences through each column fast enough (greater than 30 Hz), the matrix display appears to be stationary to a human viewer. In Figure 8.11(a), we have provided the basic configuration for the dot matrix display for a single display device. However, this basic idea can be expanded in both dimensions to provide a multicharacter, multi-line display. A larger display does not require a significant number of microcontroller pins for the interface. The dot matrix display may be used to display alphanumeric data as well as graphics data. In Figure 8.11(b), we have provided additional detail of the interface circuit.

8.5.6

LIQUID CRYSTAL CHARACTER DISPLAY (LCD) IN C

An LCD is an output device to display text information as shown in Figure 8.12. LCDs come in a wide variety of configurations, including multi-character, multi-line format. A 16 x 2 LCD format is common. That is, it has the capability of displaying two lines of 16 characters each. The characters are sent to the LCD via American Standard Code for Information Interchange (ASCII) format a single character at a time. For a parallel configured LCD, an eight bit data path and two lines are required between the microcontroller and the LCD. A small microcontroller mounted to the back panel of the LCD translates the ASCII data characters and control signals to properly display the characters. LCDs are configured for either parallel or serial data transmission format. In the example provided, we use a parallel configured display. 8.5.6.1 Programming an LCD in C

Some sample C code is provided below to send data and control signals to an LCD. In this specific example, an AND671GST 1 x 16 character LCD was connected to the Atmel ATmega328 microcontroller. One 8-bit port and two extra control lines are required to connect the microcontroller to the LCD. Note: The initialization sequence for the LCD is specified within the manufacturer’s technical data. //************************************************************************* //Internal Oscillator: 1 MHz //ATMEL AVR ATmega328 //Chip Port Function I/O Source/Dest Asserted Notes


C2 C1 C0

interface circuitry

R6 R5 R4 R3 R2 R1 R0

interface circuitry

row select

microcontroller

column select

234

5 x 7 dot matrix display

column select

a) dot matrix display layout

C2:C1:C0 3

74HC137 1:8 decoder

R6

row select

5 VDC

R0 5 VDC

5 x 7 dot matrix display b) dot matrix interface details

Figure 8.11: Dot matrix display.

8.5. OUTPUT DEVICES

Vcc

235

ta /da d n ma ble ta com ena da

GND-1 VDD-2 Vo-3 RS-4 R/W-5 E-6 DB0-7 DB1-8 DB2-9 DB3-10 DB4-11 DB5-12 DB6-13 DB7-14

10K

line1

line2 AND671GST

Figure 8.12: LCD display.

//************************************************************************* //Pin 1: /Reset //Pin 2: PD0 to DB0 LCD //Pin 3: PD1 to DB1 LCD //Pin 4: PD2 to DB2 LCD //Pin 5: PD3 to DB3 LCD //Pin 6: PD4 to DB4 LCD //Pin 7: Vcc //Pin 8: Gnd //Pin 11: PD5 to DB6 LCD //Pin 12: PD6 to DB6 LCD //Pin 13: PD7 to DB7 LCD //Pin 20: AVCC to Vcc //Pin 21: AREF to Vcc //Pin 22 Gnd //Pin 27 PC4 to LCD Enable (E) //Pin 28 PC5 to LCD RS //include files************************************************************ //ATMEL register definitions for ATmega328 #include

236


//function prototypes****************************************************** void delay(unsigned int number_of_65_5ms_interrupts); void init_timer0_ovf_interrupt(void); void initialize_ports(void); //initializes ports void power_on_reset(void); //returns system to startup state void clear_LCD(void); //clears LCD display void LCD_Init(void); //initialize AND671GST LCD void putchar(unsigned char c); //send character to LCD void putcommand(unsigned char c); //send command to LCD void timer0_interrupt_isr(void); void perform_countdown(void); void clear_LCD(void); void systems_A_OK(void); void print_mission_complete(void); void convert_int_to_string_display_LCD(unsigned int total_integer_value); //program constants #define TRUE 1 #define FALSE 0 #define OPEN 1 #define CLOSE 0 #define YES 1 #define NO 0 #define SAFE 1 #define UNSAFE 0 #define ON 1 #define OFF 0 //interrupt handler definition #pragma interrupt_handler timer0_interrupt_isr:17 //main program************************************************************* //global variables void main(void) {

8.5. OUTPUT DEVICES

237

init_timer0_ovf_interrupt(); //initialize Timer0 to serve as elapsed initialize_ports(); //initialize ports perform_countdown(); delay(46); : : : systems_A_OK(); }//end main //function definitions***************************************************** //************************************************************************* //initialize_ports: provides initial configuration for I/O ports //************************************************************************* void initialize_ports(void) { DDRB = 0xff; PORTB= 0x00; DDRC = 0xff; PORTC= 0x00; DDRD = 0xff; PORTD= 0x00; }

//PORTB[7:0] //initialize //PORTC[7:0] //initialize

as output low as output low

//PORTB[7:0] as output //initialize low

//************************************************************************* //delay(unsigned int num_of_65_5ms_interrupts): this generic delay function //provides the specified delay as the number of 65.5 ms "clock ticks" from //the Timer0 interrupt. //Note: this function is only valid when using a 1 MHz crystal or ceramic // resonator //************************************************************************* void delay(unsigned int number_of_65_5ms_interrupts)

238


{ TCNT0 = 0x00; //reset timer0 delay_timer = 0; while(delay_timer <= number_of_65_5ms_interrupts) { ; } } //************************************************************************* //int_timer0_ovf_interrupt(): The Timer0 overflow interrupt is being //employed as a time base for a master timer for this project. //The internal time base is set to operate at 1 MHz and then //is divided by 256. The 8-bit Timer0 //register (TCNT0) overflows every 256 counts or every 65.5 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0 = 0x04; //divide timer0 timebase by 256, overflow occurs every 65.5ms TIMSK = 0x01; //enable timer0 overflow interrupt asm("SEI"); //enable global interrupt } //************************************************************************* //LCD_Init: initialization for an LCD connected in the following manner: //LCD: AND671GST 1x16 character display //LCD configured as two 8 character lines in a 1x16 array //LCD data bus (pin 14-pin7) ATMEL 8: PORTD //LCD RS (pin 28) ATMEL 8: PORTC[5] //LCD E (pin 27) ATMEL 8: PORTC[4] //************************************************************************* void LCD_Init(void) { delay(1); delay(1); delay(1); // output command string to initialize LCD

8.5. OUTPUT DEVICES

putcommand(0x38); delay(1); putcommand(0x38); putcommand(0x38); putcommand(0x38); putcommand(0x0C); putcommand(0x01); putcommand(0x06); putcommand(0x00); putcommand(0x00); }

239

//function set 8-bit //function set 8-bit //function set 8-bit //one line, 5x7 char //display on //display clear-1.64 ms //entry mode set //clear display, cursor at home //clear display, cursor at home

//************************************************************************* //putchar:prints specified ASCII character to LCD //************************************************************************* void putchar(unsigned char c) { DDRD = 0xff; //set PORTD as output DDRC = DDRC|0x30; //make PORTC[5:4] output PORTD = c; PORTC = (PORTC|0x20)|PORTC_pullup_mask; //RS=1 PORTC = (PORTC|0x10)|PORTC_pullup_mask;; //E=1 PORTC = (PORTC&0xef)|PORTC_pullup_mask;; //E=0 delay(1); } //************************************************************************* //putcommand: performs specified LCD related command //************************************************************************* void putcommand(unsigned char d) { DDRD = 0xff; DDRC = DDRC|0xC0; PORTC = (PORTC&0xdf)|PORTC_pullup_mask; PORTD = d; PORTC = (PORTC|0x10)|PORTC_pullup_mask; PORTC = (PORTC&0xef)|PORTC_pullup_mask;

//set PORTD as output //make PORTA[5:4] output //RS=0 //E=1 //E=0

240


delay(1); } //************************************************************************* //clear_LCD: clears LCD //************************************************************************* void clear_LCD(void) { putcommand(0x01); } //************************************************************************* //void timer0_interrupt_isr(void) //************************************************************************* void timer0_interrupt_isr(void) { delay_timer++; } //************************************************************************* //void perform_countdown(void) //************************************************************************* void perform_countdown(void) { clear_LCD(); putcommand(0x01); putcommand(0x80); putchar(’1’); putchar (’0’); delay(15);

//cursor home //DD RAM location 1 - line 1 //print 10 //delay 1s

putcommand(0x01); putcommand(0x80); putchar(’9’); delay(15);


putcommand(0x01); putcommand(0x80);

//cursor home //DD RAM location 1 - line 1

8.5. OUTPUT DEVICES

putchar(’8’); delay(15);

//print 8 //delay 1s















241

242




//BLASTOFF! putcommand(0x01);

//cursor home

putcommand(0x80); //DD RAM location 1 - line 1 putchar(’B’); putchar(’L’); putchar(’A’); putchar(’S’); putchar(’T’); putchar(’O’); putchar(’F’); putchar(’F’); putchar(’!’); } //************************************************************************* //void systems_A_OK(void) //************************************************************************* void systems_A_OK(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’S’); putchar(’Y’); putchar(’S’); putchar(’T’); putchar(’E’); putchar(’M’); putchar(’S’); putchar(’ ’); putchar(’A’); putchar(’-’); putchar(’O’); putchar(’K’); putchar(’!’); putchar(’!’); putchar(’!’); } //************************************************************************* //void print_mission_complete(void) //************************************************************************* void print_mission_complete(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’M’); putchar(’I’); putchar(’S’); putchar(’S’); putchar(’I’); putchar(’O’); putchar(’N’);

8.5. OUTPUT DEVICES

243

putcommand(0xC0);//DD RAM location 1 - line 2 putchar(’C’); putchar(’O’); putchar(’M’); putchar(’P’); putchar(’L’); putchar(’E’); putchar(’T’); putchar(’E’); putchar(’!’); } //************************************************************************* //end of file //*************************************************************************

8.5.7

LIQUID CRYSTAL CHARACTER DISPLAY (LCD) USING THE ARDUINO DEVELOPMENT ENVIRONMENT

The Arduino Development Environment provides full support to interface an Arduino UNO R3 to either a 4-bit or 8-bit configured LCD. In the 4-bit mode precious output pins are preserved for other uses over the 8-bit configuration [www.arduino.cc]. The Arduino Development Environment hosts the following LCD related functions: • Hello World: This function displays the greeting “hello world” and also displays elapsed time since the last reset. • Blink: The Blink function provides cursor control. • Cursor: This function provides control over the underscore style cursor. • Display: This function blanks the display without the loss of displayed information. • Text Direction: This function controls which direction text flows from the cursor. • Autoscroll: This function provides automatic scrolling to the new text. • Serial Input: This function accepts serial input and displays it on the LCD. • SetCursor: This function sets the cursor position on the LCD. • Scroll: This function scrolls text left and right. Rather than include the excellent Arduino resource here, the interested reader is referred to the Arduino website for sample code and full documentation [www.arduino.cc].

8.5.8

HIGH POWER DC DEVICES

A number of direct current devices may be controlled with an electronic switching device such as a MOSFET. Specifically, an N-channel enhancement MOSFET (metal oxide semiconductor field

244


effect transistor) may be used to switch a high current load on and off (such as a motor) using a low current control signal from a microcontroller as shown in Figure 8.13(a). The low current control signal from the microcontroller is connected to the gate of the MOSFET. The MOSFET switches the high current load on and off consistent with the control signal. The high current load is connected between the load supply and the MOSFET drain. It is important to note that the load supply voltage and the microcontroller supply voltage do not have to be at the same value. When the control signal on the MOSFET gate is logic high, the load current flows from drain to source. When the control signal applied to the gate is logic low, no load current flows. Thus, the high power load is turned on and off by the low power control signal from the microcontroller.

VDD load Drain from micro

Gate

Iload

Source

a) N-channel enhance MOSFET

b) solid state relay with optical interface

Figure 8.13: MOSFET circuits.

Often the MOSFET is used to control a high power motor load. A motor is a notorious source of noise. To isolate the microcontroller from the motor noise an optical isolator may be used as an interface as shown in Figure 8.13(b). The link between the control signal from the microcontroller to the high power load is via an optical link contained within a Solid State Relay (SSR). The SSR is properly biased using techniques previously discussed.

8.6

DC SOLENOID CONTROL

The interface circuit for a DC solenoid is provided in Figure 8.14. A solenoid provides a mechanical insertion (or extraction) when asserted. In the interface, an optical isolator is used between the microcontroller and the MOSFET used to activate the solenoid. A reverse biased diode is placed across the solenoid. Both the solenoid power supply and the MOSFET must have the appropriate voltage and current rating to support the solenoid requirements.

8.7. DC MOTOR SPEED AND DIRECTION CONTROL

245

DC solenoid supply voltage +

VDD

protection diode

I

R

D MOSFET G

from micro 7404

Solid State Relay

ILOAD

S

RG

Figure 8.14: Solenoid interface circuit.

8.7

DC MOTOR SPEED AND DIRECTION CONTROL

Often, a microcontroller is used to control a high power motor load. To properly interface the motor to the microcontroller, we must be familiar with the different types of motor technologies. Motor types are illustrated in Figure 8.15. • DC motor: A DC motor has a positive and negative terminal. When a DC power supply of suitable current rating is applied to the motor it will rotate. If the polarity of the supply is switched with reference to the motor terminals, the motor will rotate in the opposite direction. The speed of the motor is roughly proportional to the applied voltage up to the rated voltage of the motor. • Servo motor: A servo motor provides a precision angular rotation for an applied pulse width modulation duty cycle. As the duty cycle of the applied signal is varied, the angular displacement of the motor also varies. This type of motor is used to change mechanical positions such as the steering angle of a wheel. • Stepper motor: A stepper motor as its name implies provides an incremental step change in rotation (typically 2.5 degree per step) for a step change in control signal sequence. The motor is typically controlled by a two or four wire interface. For the four wire stepper motor, the

246


Vmotor

+

Veff Veff = Vmotor x duty cycle [%]

-

a) DC motor

+ b) Servo motor 4 control signals

1 step

interface circuitry power ground c) Stepper motor

Figure 8.15: Motor types.

microcontroller provides a four bit control sequence to rotate the motor clockwise. To turn the motor counterclockwise, the control sequence is reversed. The low power control signals are interfaced to the motor via MOSFETs or power transistors to provide for the proper voltage and current requirements of the pulse sequence.

8.7.1

DC MOTOR OPERATING PARAMETERS

Space does not allow a full discussion of all motor types. We will concentrate on the DC motor. As previously mentioned, the motor speed may be varied by changing the applied voltage. This is difficult to do with a digital control signal. However, PWM control signal techniques discussed earlier may be combined with a MOSFET interface to precisely control the motor speed. The duty cycle of the PWM signal will also be the percentage of the motor supply voltage applied to the


247

motor, and hence the percentage of rated full speed at which the motor will rotate. The interface circuit to accomplish this type of control is shown in Figure 8.16. Various portions of this interface circuit have been previously discussed. The resistor RG , typically 10 k ohm, is used to discharge the MOSFET gate when no voltage is applied to the gate. For an inductive load, a reversed biased protection diode must be across the load. The interface circuit shown allows the motor to rotate in a given direction. As previously mentioned, to rotate the motor in the opposite direction, the motor polarity must be reversed. This may be accomplished with a high power switching network called an H-bridge specifically designed for this purpose. Reference Pack and Barrett for more information on this topic.

DC motor supply voltage +

VDD

protection diode

M -

I

R

D MOSFET G from micro

7404

Solid State Relay

ILOAD

S

RG

Figure 8.16: DC motor interface.

8.7.2

H-BRIDGE DIRECTION CONTROL

For a DC motor to operate in both the clockwise and counter clockwise direction, the polarity of the DC motor supplied must be changed. To operate the motor in the forward direction, the positive battery terminal must be connected to the positive motor terminal while the negative battery terminal must be provided to the negative motor terminal. To reverse the motor direction the motor supply polarity must be reversed. An H-bridge is a circuit employed to perform this polarity switch. Low

248


power H-bridges (500 mA) come in a convenient dual in line package (e.g., 754110). For higher power motors, a H-bridge may be constructed from discrete components as shown in Figure 8.17. If PWM signals are used to drive the base of the transistors (from microcontroller pins PD4 and PD5), both motor speed and direction may be controlled by the circuit. The transistors used in the circuit must have a current rating sufficient to handle the current requirements of the motor during start and stall conditions. 12 VDC

1000uF

200

200

ZTX451

-

+

M

11DQ06

ZTX451

11DQ06

to PD4 470

ZTX551

to PD5 ZTX551

470

Figure 8.17: H-bridge control circuit.

8.7.3

SERVO MOTOR INTERFACE

The servo motor is used for a precise angular displacement. The displacement is related to the duty cycle of the applied control signal. A servo control circuit and supporting software was provided in Chapter 7.

8.7.4

STEPPER MOTOR CONTROL

Stepper motors are used to provide a discrete angular displacement in response to a control signal step. There are a wide variety of stepper motors including bipolar and unipolar types with different configurations of motor coil wiring. Due to space limitations, we only discuss the unipolar, 5 wire stepper motor. The internal coil configuration for this motor is provided in Figure 8.18(b). Often, a wiring diagram is not available for the stepper motor. Based on the wiring configuration (Reference Figure 8.18b), one can find out the common line for both coils. It will have a resistance that is one-half of all of the other coils. Once the common connection is found, one can connect the stepper motor into the interface circuit. By changing the other connections, one can determine the correct connections for the step sequence.


a) a stepper motor rotates a fixed angle per step step 1 2 3 4

b) coil configuration and step sequence 12 VDC

PORTD[7] PORTD[6] PORTD[5] PORTD[4]

10K

TIP130 10K

TIP130 10K

TIP130 10K

c) stepper motor interface circuit

Figure 8.18: Unipolar stepper motor control circuit.

TIP130

249

250


To rotate the motor either clockwise or counter clockwise, a specific step sequence must be sent to the motor control wires as shown in Figure 8.18(c). As shown in Figure 8.18(c), the control sequence is transmitted by four pins on the microcontroller. In this example, we use PORTD[7:5]. The microcontroller does not have sufficient capability to drive the motor directly. Therefore, an interface circuit is required as shown in Figure 8.18c). For a unipolar stepper motor, we employ a TIP130 power Darlington transistor to drive each coil of the stepper motor. The speed of motor rotation is determined by how fast the control sequence is completed. The TIP 30 must be powered by a supply that has sufficient capability for the stepper motor coils. Example: An ATmega324 has been connected to a JRP 42BYG016 unipolar, 1.8 degree per step, 12 VDC at 160 mA stepper motor. The interface circuit is shown in Figure 8.19. PORTD pins 7 to 4 are used to provide the step sequence. A one second delay is used between the steps to control motor speed. Pushbutton switches are used on PORTB[1:0] to assert CW and CCW stepper motion. An interface circuit consisting of four TIP130 transistors are used between the microcontroller and the stepper motor to boost the voltage and current of the control signals. Code to provide the step sequence is shown below. Provided below is a basic function to rotate the stepper motor in the forward or reverse direction. //************************************************************************* //target controller: ATMEL ATmega328 // //ATMEL AVR ATmega328PV Controller Pin Assignments //Pin 1 Reset - 1M resistor to Vdd, tact switch to ground, 1.0 uF to ground //Pin 6 PD4 - to stepper motor coil //Pin 7 Vdd - 1.0 uF to ground //Pin 8 Gnd //Pin 11 PD5 - to stepper motor coil //Pin 12 PD6 - to stepper motor coil //Pin 13 PD7 - to stepper motor coil //Pin 14 PB0 to active high RC debounced switch - CW //Pin 20 AVcc to Vdd //Pin 21 ARef to Vcc //Pin 22 Gnd to Ground //************************************************************************* //include files************************************************************ //ATMEL register definitions for ATmega328 #include #include //interrupt handler definition


Atmega328

VDD

1M


sys reset 1.0 uF

Vcc = 5.0 volts 74HC14 4.7 K

CW

470K

(1)

PB0 (2)

0.1uF

100K


VDD

3K

Vcc = 5.0 volts 74HC14 4.7 K

CCW

470K

PB1 (3) 0.1uF

(4)

100K 3K

12 VDC

TIP130 TIP130 TIP130 TIP130

c) stepper motor interface circuit

Figure 8.19: Unipolar stepper motor control circuit.

BC E TIP130 (top view)

251

252


#pragma interrupt_handler timer0_interrupt_isr:17

//function prototypes****************************************************** void initialize_ports(void); //initializes ports void read_new_input(void); //used to read input change on PORTB void init_timer0_ovf_interrupt(void); //used to initialize timer0 overflow void timer0_interrupt_isr(void); void delay(unsigned int);

//main program************************************************************* //The main program checks PORTB for user input activity. If new activity //is found, the program responds. //global unsigned unsigned unsigned

variables char old_PORTB = 0x08; //present value of PORTB char new_PORTB; //new values of PORTB int input_delay; //delay counter - increment via Timer0 //overflow interrupt

void main(void) { initialize_ports(); init_timer0_ovf_interrupt(); while(1) { _StackCheck(); read_new_input(); } }//end main

//return LED configuration to default //used to initialize timer0 overflow

//check for stack overflow //read input status changes on PORTB

//Function definitions //************************************************************************* //initialize_ports: provides initial configuration for I/O ports //************************************************************************* void initialize_ports(void)


{ //PORTB DDRB=0xfc; PORTB=0x00;

//PORTB[7-2] output, PORTB[1:0] input //disable PORTB pull-up resistors


//set PORTC[7-0] as output //init low


253


//************************************************************************* //read_new_input: functions polls PORTB for a change in status. If status //change has occurred, appropriate function for status change is called //Pin 1 PB0 to active high RC debounced switch - CW //Pin 2 PB1 to active high RC debounced switch - CCW //************************************************************************* void read_new_input(void) { new_PORTB = (PINB & 0x03); if(new_PORTB != old_PORTB){ switch(new_PORTB){ case 0x01: while((PINB & 0x03)==0x01) { PORTD = 0x80; delay(15); PORTD = 0x00; delay(1); PORTD = 0x40; delay(15); PORTD = 0x00; delay(1);

//process change in PORTB input //CW

//delay 1s //delay 65 ms

254


PORTD = 0x20; delay(15); PORTD = 0x00; delay(1); PORTD = 0x10; delay(15); PORTD = 0x00; delay(1); } break; case 0x02: while((PINB & 0x03)==0x02) { PORTD = 0x10; delay(15); PORTD = 0x00; delay(1); PORTD = 0x20; delay(15); PORTD = 0x00; delay(1); PORTD = 0x40; delay(15); PORTD = 0x00; delay(1); PORTD = 0x80; delay(15); PORTD = 0x00; delay(1); } break;

//CCW


default:; } } old_PORTB=new_PORTB;

255

//all other cases //end switch(new_PORTB) //end if new_PORTB //update PORTB

} //************************************************************************* //int_timer0_ovf_interrupt(): The Timer0 overflow interrupt is being //employed as a time base for a master timer for this project. The internal //oscillator of 8 MHz is divided internally by 8 to provide a 1 MHz time //base and is divided by 256. The 8-bit Timer0 register (TCNT0) overflows //every 256 counts or every 65.5 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0B = 0x04; //divide timer0 timebase by 256, overfl. occurs every 65.5ms TIMSK0 = 0x01; //enable timer0 overflow interrupt asm("SEI"); //enable global interrupt } //************************************************************************* //timer0_interrupt_isr: //Note: Timer overflow 0 is cleared by hardware when executing the //corresponding interrupt handling vector. //************************************************************************* void timer0_interrupt_isr(void) { input_delay++; }

//input delay processing

//************************************************************************* //void delay(unsigned int number_of_65_5ms_interrupts) //this generic delay function provides the specified delay as the number //of 65.5 ms "clock ticks" from the Timer0 interrupt. //Note: this function is only valid when using a 1 MHz crystal or ceramic // resonator //*************************************************************************

256


void delay(unsigned int number_of_65_5ms_interrupts) { TCNT0 = 0x00; //reset timer0 input_delay = 0; while(input_delay <= number_of_65_5ms_interrupts) { ; } } //*************************************************************************

8.7.5

AC DEVICES

In a similar manner, a high power alternating current (AC) load may be switched on and off using a low power control signal from the microcontroller. In this case, a Solid State Relay is used as the switching device. Solid state relays are available to switch a high power DC or AC load [Crydom]. For example, the Crydom 558-CX240D5R is a printed circuit board mounted, air cooled, single pole single throw (SPST), normally open (NO) solid state relay. It requires a DC control voltage of 3-15 VDC at 15 mA. However, this small microcontroller compatible DC control signal is used to switch 12-280 VAC loads rated from 0.06 to 5 amps [Crydom] as shown in Figure 8.20. To vary the direction of an AC motor you must use a bi-directional AC motor. A bi-directional motor is equipped with three terminals: common, clockwise, and counterclockwise.To turn the motor clockwise, an AC source is applied to the common and clockwise connections. In like manner, to turn the motor counterclockwise, an AC source is applied to the common and counterclockwise connections. This may be accomplished using two of the Crydom SSRs.

8.8

INTERFACING TO MISCELLANEOUS DEVICES

In this section, we provide a potpourri of interface circuits to connect a microcontroller to a wide variety of peripheral devices.

8.8.1

SONALERTS, BEEPERS, BUZZERS

In Figure 8.21, we provide several circuits used to interface a microcontroller to a buzzer, beeper or other types of annunciator indexannunciator devices such as a sonalert. It is important that the interface transistor and the supply voltage are matched to the requirements of the sound producing device.

257 8.8. INTERFACING TO MISCELLANEOUS DEVICES

VDD 1M

sys reset 1.0 uF


Atmega328 1 PUR - PC6 2 RXD1 - PD0 3 TXD1 - PD1 4 PD2 5 PD3 6 PD4 7 Vcc 8 GND 9 PB6 10 PB7 11 PD5 12 PD6 13 PD7 14 PB0

Figure 8.20: AC motor control circuit.

VDD

CRYDOM 3:DC+ 4:DC-

1 2

fuse

115 VAC

AC fan

258


Vcc = 12 VDC

Vcc = 5 VDC

annunciator 12 VDC, 8 mA

buzzer, 3850 Hz 5 VDC, 3-14 mA

220

220

from micro

10K

2N2222

a) 5 VDC buzzer interface

from micro

10K

2N2222

a) 12 VDC annunciator

Figure 8.21: Sonalert, beepers, buzzers.

8.8.2

VIBRATING MOTOR

A vibrating motor is often used to gain one’s attention as in a cell phone. These motors are typically rated at 3 VDC and a high current. The interface circuit shown in Figure 8.22 is used to drive the low voltage motor. Note that the control signal provided to the transistor base is 5 VDC. To step the motor supply voltage down to the motor voltage of 3 VDC, two 1N4001 silicon rectifier diodes are used in series. These diodes provide approximately 1.4 to 1.6 VDC voltage drop. Another 1N4001 diode is reversed biased across the motor and the series diode string. The motor may be turned on and off with a 5 VDC control signal from the microcontroller or a PWM signal may be used to control motor speed.

8.9

EXTENDED EXAMPLE 1: AUTOMATED FAN COOLING SYSTEM

In this section, we describe an embedded system application to control the temperature of a room or some device. The system is illustrated in Figure 8.23. An LM34 temperature sensor (PORTC[0]) is used to monitor the instantaneous temperature of the room or device of interest. The current temperature is displayed on the Liquid Crystal Display (LCD). We send a 1 KHz PWM signal to a cooling fan (M) whose duty cycle is set from 50% to 90% using the potentiometer connected to PORTC[2]. The PWM signal should last until the

8.9. EXTENDED EXAMPLE 1: AUTOMATED FAN COOLING SYSTEM

259

5 VDC

1N4001

1N4001

+

M

1N4001

3 VDC

-

240

Figure 8.22: Controlling a low voltage motor.

temperature of the LM34 cools to a value as set by another potentiometer (PORTC[1]). When the temperature of the LM34 falls below the set level, the cooling fan is shut off. If the temperature falls while the fan is active, the PWM signal should gently return to zero, and wait for further temperature changes. Provided below is the embedded code for the system. This solution was developed by Geoff Luke, UW MSEE, as a laboratory assignment for an Industrial Control class. //************************************************************************* //Geoff Luke //EE 5880 - Industrial Controls //PWM Fan Control //Last Updated: April 10, 2010 //************************************************************************* //Description: This program reads the voltage from an LM34 temperature //sensor then sends the corresponding temperature to an LCD. //If the sensed temperature is greater than the temperature designated //by a potentiometer, then a PWM signal is turned on to trigger a fan

260


Vcc = 5 V

cooling fan speed Atmega328

VDD

1M


sys reset 1.0 uF

10K


Vcc = 5 V

threshold temperature setting 10K VDD

Vcc = 5 V

LM34 temperature sensor 75 1uF

to PORTB[7:0] Vcc 10K


data

AND671GST

DC motor supply voltage +

VDD

protection diode

M -

I

R

D MOSFET G 7404

from micro

Solid State Relay

Figure 8.23: Automated fan cooling system.

RG

S

ILOAD


261

//with duty cycle designated by another potentiometer. // //Ports: // PORTB[7:0]: data output to LCD // PORTD[7:6]: LCD control pins // PORTC[2:0]: // PORTC[0]: LM34 temperature sensor // PORTC[1]: threshold temperature // PORTC[2]: fan speed // PORTD[4] : PWM channel B output // //************************************************************************* //include files************************************************************ #include //function prototypes****************************************************** void initializePorts(); void initializeADC(); unsigned int readADC(unsigned char); void LCD_init(); void putChar(unsigned char); void putcommand(unsigned char); void voltageToLCD(unsigned int); void temperatureToLCD(unsigned int); void PWM(unsigned int); void delay_5ms(); int main(void) { unsigned int tempVoltage, tempThreshold; initializePorts(); initializeADC(); LCD_init(); while(1) { tempVoltage = readADC(0);

262


temperatureToLCD(tempVoltage); tempThreshold = readADC(1); if(tempVoltage > tempThreshold) { PWM(1); while(tempVoltage > tempThreshold) { tempVoltage = readADC(0); temperatureToLCD(tempVoltage); tempThreshold = readADC(1); } OCR1BL = 0x00; } } return 0; } //************************************************************************* void { DDRD DDRC DDRB }

initializePorts() = 0xFF; = 0xFF; = 0xFF;

//************************************************************************* void initializeADC() { //select channel 0 ADMUX = 0; //enable ADC and set module enable ADC and //set module prescalar to 8 ADCSRA = 0xC3; //Wait until conversion is ready while(!(ADCSRA & 0x10));


263

//Clear conversion ready flag ADCSRA |= 0x10; } //************************************************************************* unsigned int readADC(unsigned char channel) { unsigned int binary_weighted_voltage, binary_weighted_voltage_low; unsigned int binary_weighted_voltage_high; //weighted binary ADMUX = channel; ADCSRA |= 0x43;

//Select channel //Start conversion

while (!(ADCSRA & 0x10)); ADCSRA |= 0x10;

//Set ADC module prescalar to 8 //critical accurate ADC results //Check if conversion is ready //Clear conv rdy flag - set the bit

binary_weighted_voltage_low = ADCL; //Read 8 low bits first (important) //Read 2 high bits, multiply by 256 binary_weighted_voltage_high = ((unsigned int)(ADCH << 8)); binary_weighted_voltage = binary_weighted_voltage_low + binary_weighted_voltage_high; return binary_weighted_voltage; }

//ADCH:ADCL

//************************************************************************* //LCD_Init: initialization for an LCD connected in the following manner: //LCD: AND671GST 1x16 character display //LCD configured as two 8 character lines in a 1x16 array //LCD data bus (pin 14-pin7) ATMEL ATmega16: PORTB //LCD RS (pin 4) ATMEL ATmega16: PORTD[7] //LCD E (pin 6) ATMEL ATmega16: PORTD[6] //*************************************************************************

264


void LCD_init(void) { delay_5ms(); delay_5ms(); delay_5ms();

putcommand(0x38); delay_5ms(); putcommand(0x38); delay_5ms(); putcommand(0x38); putcommand(0x38); putcommand(0x0E); putcommand(0x01); putcommand(0x06); putcommand(0x00); putcommand(0x00); }

// output command string to //initialize LCD //function set 8-bit //function set 8-bit //function set 8-bit //one line, 5x7 char //display on //display clear-1.64 ms //entry mode set //clear display, cursor at home //clear display, cursor at home

//************************************************************************* //putchar:prints specified ASCII character to LCD //************************************************************************* void putChar(unsigned char c) { DDRB = 0xff; //set PORTB as output DDRD = DDRD|0xC0; //make PORTD[7:6] output PORTB = c; PORTD = PORTD|0x80; //RS=1 PORTD = PORTD|0x40; //E=1 PORTD = PORTD&0xbf; //E=0 delay_5ms(); } //*************************************************************************


265

//performs specified LCD related command //************************************************************************* void putcommand(unsigned char d) { DDRB = 0xff; //set PORTB as output DDRD = DDRD|0xC0; //make PORTD[7:6] output PORTD = PORTD&0x7f; //RS=0 PORTB = d; PORTD = PORTD|0x40; //E=1 PORTD = PORTD&0xbf; //E=0 delay(); }

//************************************************************************* //delay //************************************************************************* void delay(void) { unsigned int i; for(i=0; i<2500; i++) { asm("nop"); } } //************************************************************************* void voltageToLCD(unsigned int ADCValue) { float voltage; unsigned int ones, tenths, hundredths; voltage = (float)ADCValue*5.0/1024.0; ones = (unsigned int)voltage;

266


tenths = (unsigned int)((voltage-(float)ones)*10); hundredths = (unsigned int)(((voltage-(float)ones)*10-(float)tenths)*10); putcommand(0x80); putChar((unsigned char)(ones)+48); putChar(’.’); putChar((unsigned char)(tenths)+48); putChar((unsigned char)(hundredths)+48); putChar(’V’); putcommand(0xC0); } //************************************************************************* void temperatureToLCD(unsigned int ADCValue) { float voltage,temperature; unsigned int tens, ones, tenths; voltage = (float)ADCValue*5.0/1024.0; temperature = voltage*100; tens = (unsigned int)(temperature/10); ones = (unsigned int)(temperature-(float)tens*10); tenths = (unsigned int)(((temperature-(float)tens*10)-(float)ones)*10); putcommand(0x80); putChar((unsigned char)(tens)+48); putChar((unsigned char)(ones)+48); putChar(’.’); putChar((unsigned char)(tenths)+48); putChar(’F’); } //************************************************************************* void PWM(unsigned int PWM_incr)


{ unsigned int fan_Speed_int; float fan_Speed_float; int PWM_duty_cycle; fan_Speed_int = readADC(0x02); //fan Speed Setting //unsigned int convert to max duty cycle setting: // 0 VDC = 50% = 127, // 5 VDC = 100% = 255 fan_Speed_float = ((float)(fan_Speed_int)/(float)(0x0400)); //convert volt to PWM constant 127-255 fan_Speed_int = (unsigned int)((fan_Speed_float * 127) + 128.0); //Configure PWM clock TCCR1A = 0xA1; TCCR1B = 0x02;

//freq = resonator/510 = 4 MHz/510 //freq = 19.607 kHz //clock source //division of 8: 980 Hz

//Initiate PWM duty cycle variables PWM_duty_cycle = 0; OCR1BH = 0x00; OCR1BL = (unsigned char)(PWM_duty_cycle);//set PWM duty cycle Ch B to 0% //Ramp up to fan Speed in 1.6s OCR1BL = (unsigned char)(PWM_duty_cycle);//set PWM duty cycle Ch B while (PWM_duty_cycle < fan_Speed_int) { if(PWM_duty_cycle < fan_Speed_int) //increment duty cycle PWM_duty_cycle=PWM_duty_cycle + PWM_incr; //set PWM duty cycle Ch B OCR1BL = (unsigned char)(PWM_duty_cycle); } }

267

268


//*************************************************************************

8.10 EXTENDED EXAMPLE 2: FINE ART LIGHTING SYSTEM In Chapter 2 and 5, we investigated an illumination system for a painting. The painting was to be illuminated via high intensity white LEDs. The LEDs could be mounted in front of or behind the painting as the artist desired. In Chapter 5, we equipped the lighting system with an IR sensor to detect the presence of someone viewing the piece. We also wanted to adjust the intensity of the lighting based on how the close viewer was to the art piece. In this example, we enhance the lighting system with three IR sensors. The sensors will determine the location of viewers and illuminate portions of the painting accordingly. The analogWrite function is used to set the intensity of the LEDs using PWM techniques. The Arduino Development Environment sketch to sense how away the viewer is and issue a proportional intensity control signal to illuminate the LED is provided below. The analogRead function is used to obtain the signal from the IR sensor. The analogWrite function is used to issue a proportional signal. //************************************************************************* //analog input pins #define left_IR_sensor 0 //analog pin - left IR sensor #define center_IR_sensor 1 //analog pin - center IR sensor #define right_IR_sensor 2 //analog pin - right IR sensor

#define col_0_control #define col_1_control #define col_2_control

0 1 2

//digital output pins //LED indicators - wall detectors //digital pin - column 0 control //digital pin - column 1 control //digital pin - column 2 control

int left_IR_sensor_value; int center_IR_sensor_value;

//declare var. for left IR sensor //declare var. for center IR sensor

int right_IR_sensor_value;

//declare var. for right IR sensor

void setup() { pinMode(col_0_control, OUTPUT); pinMode(col_1_control, OUTPUT); pinMode(col_2_control, OUTPUT);

//LED indicators - wall detectors //configure pin 0 for digital output //configure pin 1 for digital output //configure pin 2 for digital output

Figure 8.24: IR sensor interface. 5 VDC

IR sensor left

Column 2 control Column 1 control Column 0 control A0

5VGnd

IR sensor middle 5 VDC

ANALOG IN 0 123 4 5

Arduino UNO R3

3 21 0 9 8 76 5 4 32 1 0 1 1 1 1 DIGITAL

A1

Column 0 control

10K

10K

10K

10K

10K

10K

A2

Column 1 control

5 VDC

IR sensor right

2N2222

R

9 VDC

2N2222

R

9 VDC

2N2222

R

9 VDC

male header pins

2N2222

R

Column 2 control

10K

10K

10K

Sensor connection: - Red: 5 VDC - Yellow: Signal output - Black: Ground

9 VDC

2N2222

R

9 VDC

2N2222

R

9 VDC

2N2222

R

9 VDC

2N2222

R

9 VDC

2N2222

R

9 VDC

8.10. EXTENDED EXAMPLE 2: FINE ART LIGHTING SYSTEM 269

270


} void loop() { //read analog output from IR sensors left_IR_sensor_value = analogRead(left_IR_sensor); center_IR_sensor_value = analogRead(center_IR_sensor); right_IR_sensor_value = analogRead(right_IR_sensor); if(left_IR_sensor_value < 128) { analogWrite(col_0_control, 31); } else if(left_IR_sensor_value < 256) { analogWrite(col_0_control, 63); } else if(left_IR_sensor_value < 384) { analogWrite(col_0_control, 95); } else if(left_IR_sensor_value < 512) { analogWrite(col_0_control, 127); } else if(left_IR_sensor_value < 640) { analogWrite(col_0_control, 159); } else if(left_IR_sensor_value < 768) { analogWrite(col_0_control, 191); } else if(left_IR_sensor_value < 896) { analogWrite(col_0_control, 223); } else








8.10. EXTENDED EXAMPLE 2: FINE ART LIGHTING SYSTEM

{ analogWrite(col_0_control, 255); }


if(center_IR_sensor_value < 128) { analogWrite(col_1_control, 31); //0 } else if(center_IR_sensor_value < 256) { analogWrite(col_1_control, 63); //0 } else if(center_IR_sensor_value < 384) { analogWrite(col_1_control, 95); //0 } else if(center_IR_sensor_value < 512) { analogWrite(col_1_control, 127); //0 } else if(center_IR_sensor_value < 640) { analogWrite(col_1_control, 159); //0 } else if(center_IR_sensor_value < 768) { analogWrite(col_1_control, 191); //0 } else if(center_IR_sensor_value < 896) { analogWrite(col_1_control, 223); //0 } else { analogWrite(col_1_control, 255); //0 } if(right_IR_sensor_value < 128) {

(off) to 255 (full speed)








271

272


analogWrite(col_2_control, 31); //0 } else if(right_IR_sensor_value < 256) { analogWrite(col_2_control, 63); //0 } else if(right_IR_sensor_value < 384) { analogWrite(col_2_control, 95); //0 } else if(right_IR_sensor_value < 512) { analogWrite(col_2_control, 127); //0 } else if(right_IR_sensor_value < 640) { analogWrite(col_2_control, 159); //0 } else if(right_IR_sensor_value < 768) { analogWrite(col_2_control, 191); //0 } else if(right_IR_sensor_value < 896) { analogWrite(col_2_control, 223); //0 } else { analogWrite(col_2_control, 255); //0 } delay(500); }









//delay 500 ms

//*************************************************************************

8.11 EXTENDED EXAMPLE 3: FLIGHT SIMULATOR PANEL We close the chapter with an extended example of developing a flight simulator panel.This panel was actually designed and fabricated for a middle school to allow students to react to space mission like

8.11. EXTENDED EXAMPLE 3: FLIGHT SIMULATOR PANEL

273

status while using a program that allowed them to travel about the planets. An Atmel ATmega328 microcontroller is used because its capabilities best fit the requirements for the project. The panel face is shown in Figure 8.25. It consists of a joystick that is connected to a host computer for the flight simulator software. Below the joystick is a two line liquid crystal display equipped with a backlight LED (Hantronix HDM16216L-7, Jameco# 658988). Below the LCD is a buzzer to alert students to changing status. There are also a complement of other status indicators. From left-to-right is the Trip Duration potentiometer. At the beginning of the flight episode students are prompted to set this from 0 to 60 minutes to communicate to the microcontroller the length of the flight episode. This data is used to calculate different flight increments. There are also a series of simulated circuit breakers: system reset (SYS Reset), oxygen (O2 CB), auxiliary fuel (AUX FUEL CB), and the main power circuit breakers (MAIN PWR CB). These are not actual circuit breakers but normally open (NO) single pole single throw (SPST) momentary pushbutton switches that allow the students to interact with the microcontroller. There are also a series of LEDs that form a Y pattern on the panel face. They are also used to indicate status changes. To interface the flight simulator panel to the microcontroller a number of different techniques previously discussed in the book were employed. The interface diagram is shown in Figure 8.26. Pin 1 is a reset for the microcontroller. When the switch is depressed, pin 1 is taken low and resets the microcontroller. Port D of the microcontroller (pins 2-6, 11-13) forms the data connection for the LCD. Pin 9 is used to turn the buzzer on and off. This pin is routed through a transistor interface described earlier in the text. Port B[5:0] (pins 14-19) is used to control the LEDs on the front panel. Each individual LED is also supported with a transistor interface circuit. Conveniently, these small NPN signal transistors come in four to a 14 pin DIP package (MPQ2222). Port C [0] (pin 23) is used as an analog input pin. It is connected to the trip duration potentiometer. Port C pins [3:1] (pins 24 to 26) are used to connect the NO SPST tact switches to the microcontroller. Port C pins [4:5] (pins 27, 28) are used for the LCD control signals. The software flowchart is shown in Figure 8.27. After startup the students are prompted via the LCD display to set the trip duration and then press the main power circuit breaker. This potentiometer setting is then used to calculate four different trip increments. Countdown followed by blastoff then commences. At four different trip time increments, students are presented with status that they must respond to. Real clock time is kept using the TCNT0 timer overflow configured as a 65.5 ms “clock tick.” The overall time base for the microcontroller was its internal 1 MHz clock that may be selected during programming with the STK500. Provided below is the code listing for the flight simulator panel. //************************************************************************* //file name: flight_sim.c //author: Steve Barrett, Ph.D., P.E. //last revised: April 10, 2010 //function: Controls Flight Simulator Control Panel for Larimer County // School District #1 //

274


Joystick

Status Panel

TRIP TIME: 0-60m SET MAIN PWR CB buzzer

(PB6)

(PB5) (PB3) (PB2)

(PB4)

(PB1)

Trip Duration SYS Reset

Figure 8.25: Flight Simulator Panel.

MAIN PWR CB

(PB0) O2 CB

AUX FUEL CB

line 2

line1

5 VDC

Figure 8.26: Interface diagram for the flight simulator panel.

PB0

2

LED0

data

RS

PB1

6

LED1

220 DIP resistor

5V

10K DIP resistor

3

1

+

Vcc

E

5

7

+

Vcc

system reset

LED

LED K-16 LED A-15 GND-1 VDD-2 Vo-3 RS-4 R/W-5 E-6 DB0-7 DB1-8 DB2-9 DB3-10 DB4-11 DB5-12 DB6-13 DB7-14

contrast

1M

PB2

LED6

Vcc

DB0 DB1 DB2 DB3 DB4

9

LED2

10

8

+

Vcc

LED0

DB7

DB5 DB6

piezo buzzer

1 uF

PB3

13

LED3

12

14

+

Vcc

PB4

2

LED4

3

1

+

Vcc

6

LED5

5

7

+

Vcc

LED2 LED1

LED5 LED4 LED3

Vcc

Vcc

Engine Power

PB6

O2 Circuit Breaker

RS E AUX Fuel

PB5

1-(/Reset) PC6 PC5-28 2-PD0 PC4-27 3-PD1 PC3-26 4-PD2 PC2-25 ATmega328 5-PD3 PC1-24 6-PD4 PC0 (ADC0)-23 7-VCC GND-22 8-GND AREF-21 9-PB6 AVCC-20 10-PB7 PB5-19 11-PD5 PB4-18 12-PD6 PB3-17 13-PD7 PB2-16 14-PB0 PB1-15

9

LED6

10

8

+

Vcc

PB7

13

3-14 mA

5 VDC,

3850 Hz

buzzer

trip duration pot

Vcc = 5 VDC

12

14

Vcc

8.11. EXTENDED EXAMPLE 3: FLIGHT SIMULATOR PANEL 275

Figure 8.27: Software flow for the flight simulator panel.

delay(3s)

LED_blastoff_seq

perform_countdown

calculate_trip_inc (25...)

main pwr set? yes read_ADC

no

100% trip time?

no

75% trip time?

no

50% trip time?

no

25% trip time?

while(1)

SYSTEMS A-OK

no

SET MAIN PWR CB

TRIP TIME 0-60m

initialize_LCD

initialize_ADC

initialize_ports

initialize_timer

sound_alarm

flt100_actions

sound_alarm

flt75_actions

flt50_actions sound_alarm

sound_alarm

flt25_actions

flash_LED_panel

flash_LED_panel

flash_LED_panel

flash_LED_panel

FUEL EXPENDED MISSION ABORT

POWER DOWN 30S

ENGINE OVERHEAT

ASSERT AUX FUEL

***LOW FUEL***

RESET O2 CB

***LOW O2***

no

yes

yes

yes

LED_power_down_seq

actions_complete?

actions_complete?

actions_complete?

SYS A-OK

SYS A-OK

SYS A-OK

reset_alarm

reset_alarm

reset_alarm

restore_panel

restore_panel

restore_panel

276 8. ATMEL AVR OPERATING PARAMETERS AND INTERFACING


277

//ATMEL AVR ATmega328 //Chip Port Function I/O Source/Dest Asserted Notes //************************************************************************* //Pin 1: /Reset //Pin 2: PD0 to DB0 LCD //Pin 3: PD1 to DB1 LCD //Pin 4: PD2 to DB2 LCD //Pin 5: PD3 to DB3 LCD //Pin 6: PD4 to DB4 LCD //Pin 7: Vcc //Pin 8: Gnd //Pin 9: PB6 to LED6 //Pin 10: PB7 to piezo buzzer //Pin 11: PD5 to DB6 LCD //Pin 12: PD6 to DB6 LCD //Pin 13: PD7 to DB7 LCD //Pin 14: PB0 to LED0 //Pin 15: PB1 to LED1 //Pin 16: PB2 to LED2 //Pin 17: PB3 to LED3 //Pin 18: PB4 to LED4 //Pin 19: PB5 to LED5 //Pin 20: AVCC to Vcc //Pin 21: AREF to Vcc //Pin 22 Gnd //Pin 23 ADC0 to trip duration potentiometer //Pin 24 PC1 Engine Power Switch //Pin 25 PC2 AUX Fuel circuit breaker //Pin 26 PC3 O2 circuit breaker //Pin 27 PC4 to LCD Enable (E) //Pin 28 PC5 to LCD RS // //include files************************************************************ //ATMEL register definitions for ATmega8 #include

278


//function prototypes****************************************************** void delay(unsigned int number_of_65_5ms_interrupts); void init_timer0_ovf_interrupt(void); void InitADC(void); //initialize ADC void initialize_ports(void); //initializes ports void power_on_reset(void); //returns system to startup state unsigned int ReadADC(unsigned char chan);//read value from ADC results void clear_LCD(void); //clears LCD display void LCD_Init(void); //initialize AND671GST LCD void putchar(unsigned char c); //send character to LCD void putcommand(unsigned char c); //send command to LCD unsigned int ReadADC(unsigned char chan);//read value from ADC results void timer0_interrupt_isr(void); void flt25_actions(void); void flt50_actions(void); void flt75_actions(void); void flt100_actions(void); void sound_alarm(void); void turn_off_LEDs(void); void reset_alarm(void); void restore_panel(void); void LED_blastoff_sequence(void); void LED_power_down_sequence(void); void monitor_main_power_CB(void); void monitor_O2_CB_reset(void); void monitor_aux_fuel_CB(void); void perform_countdown(void); void print_LOWO2(void); void print_LOW_FUEL(void); void print_fuel_expended(void); void print_OVERHEAT(void); void print_trip_dur(void); void flash_LED_panel(void); void clear_LCD(void); void calculate_trip_int(void); void systems_A_OK(void); //program constants


#define #define #define #define #define #define #define #define #define #define

279

TRUE 1 FALSE 0 OPEN 1 CLOSE 0 YES 1 NO 0 SAFE 1 UNSAFE 0 ON 1 OFF 0

//interrupt handler definition #pragma interrupt_handler timer0_interrupt_isr:17 //main program************************************************************* //global variables unsigned int flt_25, flt_50, flt_75, flt_100; unsigned int action25_done=NO, action50_done=NO; unsigned int action75_done=NO, action100_done=NO; unsigned int achieved25=NO, achieved50=NO; unsigned int achieved75=NO, achieved100=NO; unsigned int flt_timer=0; unsigned int trip_duration_volt; unsigned char PORTC_pullup_mask = 0x0e; unsigned int flash_timer; unsigned int PORTB_LEDs; unsigned int flash_panel=NO; unsigned int delay_timer; unsigned int troubleshooting = 1; void convert_display_voltage_LCD(int trip_duration_volt); void convert_int_to_string_display_LCD(unsigned int total_integer_value); void main(void) { init_timer0_ovf_interrupt(); //initialize Timer0 to serve as elapsed initialize_ports(); //initialize ports InitADC(); //initialize ADC

280


LCD_Init(); print_trip_dur(); //prompt user to enter trip duration monitor_main_power_CB(); clear_LCD();

//initialize LCD

trip_duration_volt = ReadADC(0x00); //Read trip duration ADC0 if(troubleshooting) { //display voltage LCD convert_display_voltage_LCD(trip_duration_volt); delay(46); } calculate_trip_int(); if(troubleshooting) { convert_int_to_string_display_LCD(flt_25); delay(46); } perform_countdown(); LED_blastoff_sequence(); sound_alarm(); delay(46); reset_alarm(); systems_A_OK(); while(1) { if(flt_timer if(flt_timer if(flt_timer if(flt_timer

> > > >

flt_25) flt_50) flt_75) flt_100)

achieved25 achieved50 achieved75 achieved100

= = = =

YES; YES; YES; YES;

if((achieved25==YES)&&(action25_done==NO)) //25% flight complete { flt25_actions(); action25_done=YES; systems_A_OK(); }


281

if((achieved50==YES)&&(action50_done==NO)) //50% flight complete { flt50_actions(); action50_done=YES; systems_A_OK(); } if((achieved75==YES)&&(action75_done==NO)) //75% flight complete { flt75_actions(); action75_done=YES; systems_A_OK(); } if((achieved100==YES)&&(action100_done==NO)) //100% flight complete { flt100_actions(); action100_done=YES; } }//end while }//end main //function definitions***************************************************** //************************************************************************* //initialize_ports: provides initial configuration for I/O ports // //Note: when the RSTDISBL fuse is unprogrammed, the RESET circuitry is // connected to the pin, and the pin can not be used as an I/O pin. //************************************************************************* void initialize_ports(void) { DDRB = 0xff; //PORTB[7:0] as output PORTB= 0x00; //initialize low

282


DDRC = 0xb0; PORTC= PORTC_pullup_mask; DDRD = 0xff; PORTD =0x00; }

//set PORTC as output OROO_IIII 1011_0000 //initialize pullups PORTC[3:1] //set PORTD as output //initialize low

//************************************************************************* //delay(unsigned int num_of_65_5ms_interrupts): this generic delay function //provides the specified delay as the number of 65.5 ms "clock ticks" //from the Timer0 interrupt. //Note: this function is only valid when using a 1 MHz crystal or ceramic // resonator //************************************************************************* void delay(unsigned int number_of_65_5ms_interrupts) { TCNT0 = 0x00; //reset timer0 delay_timer = 0; while(delay_timer <= number_of_65_5ms_interrupts) { ; } } //************************************************************************* //InitADC: initialize ADC converter //************************************************************************* void InitADC( void) { ADMUX = 0; ADCSRA = 0xC3;

//Select channel 0 //Enable ADC & start 1st dummy conversion //Set ADC module prescalar to 8 //critical for accurate ADC results while (!(ADCSRA & 0x10)); //Check if conversation is ready ADCSRA |= 0x10; //Clear conv rdy flag - set the bit } //*************************************************************************


283

//ReadADC: read analog voltage from ADC-the desired channel for conversion //is passed in as an unsigned character variable. The result is returned //as a left justified, 10 bit binary result. //The ADC prescalar must be set to 8 to slow down the ADC clock at higher //external clock frequencies (10 MHz) to obtain accurate results. //************************************************************************* unsigned int ReadADC(unsigned char channel) { unsigned int binary_weighted_voltage, binary_weighted_voltage_low; //weighted binary voltage unsigned int binary_weighted_voltage_high; ADMUX = channel; ADCSRA |= 0x43;

//Select channel //Start conversion //Set ADC module prescalar to 8

//critical for accurate ADC results while (!(ADCSRA & 0x10)); //Check if conversion is ready ADCSRA |= 0x10; //Clear Conv rdy flag - set the bit binary_weighted_voltage_low = ADCL; //Read 8 low bits first (important) //Read 2 high bits, multiply by 256 binary_weighted_voltage_high = ((unsigned int)(ADCH << 8)); binary_weighted_voltage=binary_weighted_voltage_low | binary_weighted_voltage_high; return binary_weighted_voltage; //ADCH:ADCL } //************************************************************************* //int_timer0_ovf_interrupt(): The Timer0 overflow interrupt is being //employed as a time base for a master timer for this project. //The internal time base is set to operate at 1 MHz and then //is divided by 256. The 8-bit Timer0 register (TCNT0) overflows //every 256 counts or every 65.5 ms. //************************************************************************* void init_timer0_ovf_interrupt(void) { TCCR0 = 0x04; //divide timer0 timebase by 256, overfl. occurs every 65.5ms TIMSK = 0x01; //enable timer0 overflow interrupt

284


asm("SEI"); }

//enable global interrupt

//************************************************************************* //LCD_Init: initialization for an LCD connected in the following manner: //LCD: AND671GST 1x16 character display //LCD configured as two 8 character lines in a 1x16 array //LCD data bus (pin 14-pin7) ATMEL 8: PORTD //LCD RS (pin 28) ATMEL 8: PORTC[5] //LCD E (pin 27) ATMEL 8: PORTC[4] //************************************************************************* void LCD_Init(void) { delay(1); delay(1); delay(1); // output command string to initialize LCD putcommand(0x38); //function set 8-bit delay(1); putcommand(0x38); //function set 8-bit putcommand(0x38); //function set 8-bit putcommand(0x38); //one line, 5x7 char putcommand(0x0C); //display on putcommand(0x01); //display clear-1.64 ms putcommand(0x06); //entry mode set putcommand(0x00); //clear display, cursor at home putcommand(0x00); //clear display, cursor at home } //************************************************************************* //putchar:prints specified ASCII character to LCD //************************************************************************* void putchar(unsigned char c) { DDRD = 0xff; DDRC = DDRC|0x30; PORTD = c;

//set PORTD as output //make PORTC[5:4] output


PORTC = (PORTC|0x20)|PORTC_pullup_mask; PORTC = (PORTC|0x10)|PORTC_pullup_mask;; PORTC = (PORTC&0xef)|PORTC_pullup_mask;; delay(1); }

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//RS=1 //E=1 //E=0

//************************************************************************* //putcommand: performs specified LCD related command //************************************************************************* void putcommand(unsigned char d) { DDRD = 0xff; DDRC = DDRC|0xC0; PORTC = (PORTC&0xdf)|PORTC_pullup_mask; PORTD = d; PORTC = (PORTC|0x10)|PORTC_pullup_mask; PORTC = (PORTC&0xef)|PORTC_pullup_mask; delay(1); }

//set PORTD as output //make PORTA[5:4] output //RS=0 //E=1 //E=0

//************************************************************************* //clear_LCD: clears LCD //************************************************************************* void clear_LCD(void) { putcommand(0x01); } //************************************************************************* //*void calculate_trip_int(void) //************************************************************************* void calculate_trip_int(void) { unsigned int trip_duration_sec; unsigned int trip_duration_int;

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trip_duration_sec=(unsigned int)(((double)(trip_duration_volt)/1024.0)* 60.0*60.0); trip_duration_int = (unsigned int)((double)(trip_duration_sec)/0.0655); flt_25 = (unsigned int)((double)(trip_duration_int) * 0.25); flt_50 = (unsigned int)((double)(trip_duration_int) * 0.50); flt_75 = (unsigned int)((double)(trip_duration_int) * 0.75); flt_100 = trip_duration_int; } //************************************************************************* //void timer0_interrupt_isr(void) //************************************************************************* void timer0_interrupt_isr(void) { delay_timer++; flt_timer++; //increment flight timer if(flash_panel==YES) { if(flash_timer <= 8) { flash_timer++; } else { flash_timer = 0; if(PORTB_LEDs == OFF) { PORTB = 0xff; PORTB_LEDs = ON; } else { PORTB = 0x00; PORTB_LEDs = OFF; } } }


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else { flash_timer = 0; } } //************************************************************************* //void flt25_actions(void) //************************************************************************* void flt25_actions(void) { sound_alarm(); flash_LED_panel(); print_LOWO2(); monitor_O2_CB_reset(); reset_alarm(); restore_panel(); action25_done = YES; } //************************************************************************* //void flt50_actions(void) //************************************************************************* void flt50_actions(void) { sound_alarm(); flash_LED_panel(); print_LOW_FUEL(); monitor_aux_fuel_CB(); reset_alarm(); restore_panel(); action50_done = YES; } //************************************************************************* //void flt75_actions(void) //*************************************************************************

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void flt75_actions(void) { sound_alarm(); flash_LED_panel(); print_OVERHEAT(); delay(458); monitor_main_power_CB(); reset_alarm(); restore_panel(); action75_done = YES; }

//delay 30s

//************************************************************************* //void flt100_actions(void) //************************************************************************* void flt100_actions(void) { sound_alarm(); flash_LED_panel(); print_fuel_expended(); turn_off_LEDs(); action100_done = YES; }

//************************************************************************* //void sound_alarm(void) //************************************************************************* void sound_alarm(void) { PORTB = PORTB | 0x80; } //************************************************************************* //void turn_off_LEDs(void) //*************************************************************************


289

void turn_off_LEDs(void) { PORTB = PORTB & 0x80; }

//************************************************************************* //void reset_alarm(void) //************************************************************************* void reset_alarm(void) { PORTB = PORTB & 0x7F; } //************************************************************************* //void restore_panel(void) //************************************************************************* void restore_panel(void) { flash_panel = NO; PORTB = PORTB | 0x7F; } //************************************************************************* //void LED_blastoff_sequence(void) //************************************************************************* void LED_blastoff_sequence(void) { PORTB = 0x00; //0000_0000 delay(15); //delay 1s PORTB = 0x01; //0000_0001 delay(15); //delay 1s PORTB = 0x03; //0000_0011 delay(15); //delay 1s PORTB = 0x07; //0000_0111

290


delay(15); PORTB = 0x1F; delay(15); PORTB = 0x7F; delay(15); }

//delay 1s //0001_1111 //delay 1s //0111_1111 //delay 1s

//************************************************************************* //void LED_power_down_sequence(void) //************************************************************************* void LED_power_down_sequence(void) { PORTB = 0x7F; //0111_1111 delay(15); //delay 1s PORTB = 0x1F; //0001_1111 delay(15); //delay 1s PORTB = 0x07; //0000_0111 delay(15); //delay 1s PORTB = 0x03; //0000_0011 delay(15); //delay 1s PORTB = 0x01; //0000_0001 delay(15); //delay 1s PORTB = 0x00; //0000_0000 delay(15); //delay 1s } //************************************************************************* //void monitor_main_power_CB(void) //************************************************************************* void monitor_main_power_CB(void) { while((PINC & 0x02) == 0x02) { ; //wait for PC1 to be exerted low } }


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//************************************************************************* //void monitor_O2_CB_reset(void) //************************************************************************* void monitor_O2_CB_reset(void) { while((PINC & 0x08) == 0x08) { ; //wait for PC3 to be exerted low } } //************************************************************************* //void monitor_aux_fuel_CB(void) //************************************************************************* void monitor_aux_fuel_CB(void) { while((PINC & 0x04) == 0x04) { ; //wait for PC2 to be exerted low } } //************************************************************************* //void perform_countdown(void) //************************************************************************* void perform_countdown(void) { clear_LCD(); putcommand(0x01); putcommand(0x80); putchar(’1’); putchar (’0’); delay(15);


putcommand(0x01); putcommand(0x80); putchar(’9’);

//cursor home //DD RAM location 1 - line 1 //print 9

292


delay(15);

//delay 1s













putcommand(0x01);

//cursor home

putcommand(0x80); putchar(’2’); delay(15);

//DD RAM location 1 - line 1 //print 2 //delay 1s

putcommand(0x01);

//cursor home


putcommand(0x80); putchar(’1’); delay(15);

//DD RAM location 1 - line 1 //print 1 //delay 1s



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//BLASTOFF! putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’B’); putchar(’L’); putchar(’A’); putchar(’S’); putchar(’T’); putchar(’O’); putchar(’F’); putchar(’F’); putchar(’!’); } //************************************************************************* //void print_LOWO2(void) //************************************************************************* void print_LOWO2(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’L’); putchar(’O’); putchar(’W’); putchar(’ ’); putchar(’O’); putchar(’2’); putcommand(0xC0);//DD RAM location 1 - line 2 putchar(’R’); putchar(’E’); putchar(’S’); putchar(’E’); putchar(’T’); putchar(’ ’); putchar(’O’); putchar(’2’); putchar(’ ’); putchar(’C’); putchar(’B’); } //************************************************************************* //void print_LOW_FUEL(void) //*************************************************************************

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void print_LOW_FUEL(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’L’); putchar(’O’); putchar(’W’); putchar(’ ’); putchar(’F’); putchar(’U’); putchar(’E’); putchar(’L’); putcommand(0xC0);//DD RAM location 1 - line 2 putchar(’A’); putchar(’S’); putchar(’S’); putchar(’E’); putchar(’R’); putchar(’T’); putchar(’ ’); putchar(’A’); putchar(’U’); putchar(’X’); putchar(’F’); putchar(’U’); putchar(’E’); putchar(’L’); putchar(’C’); putchar(’B’); } //************************************************************************* //void print_fuel_expended(void) //************************************************************************* void print_fuel_expended(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’F’); putchar(’U’); putchar(’E’); putchar(’L’); putchar(’ ’); putchar(’E’); putchar(’X’); putchar(’P’); putchar(’E’); putchar(’N’); putchar(’D’); putchar(’E’); putchar(’D’); putcommand(0xC0);//DD RAM location 1 - line 2 putchar(’S’); putchar(’H’); putchar(’U’); putchar(’T’); putchar(’T’); putchar(’I’); putchar(’N’); putchar(’G’); putchar(’ ’); putchar(’D’); putchar(’O’); putchar(’W’); putchar(’N’); putchar(’.’); putchar(’.’); putchar(’.’); } //************************************************************************* //void print_trip_dur(void); //*************************************************************************


295

void print_trip_dur(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’T’); putchar(’R’); putchar(’I’); putchar(’P’); putchar(’T’); putchar(’I’); putchar(’M’); putchar(’E’); putchar(’:’); putchar(’0’); putchar(’-’); putchar(’6’); putchar(’0’); putcommand(0xC0);//DD RAM location 1 - line 2 putchar(’S’); putchar(’E’); putchar(’T’); putchar(’ ’); putchar(’M’); putchar(’A’); putchar(’I’); putchar(’N’); putchar(’ ’); putchar(’P’); putchar(’W’); putchar(’R’); putchar(’ ’); putchar(’C’); putchar(’B’); }

//************************************************************************* //void print_OVERHEAT(void) //************************************************************************* void print_OVERHEAT(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’E’); putchar(’N’); putchar(’G’); putchar(’I’); putchar(’N’); putchar(’E’); putchar(’ ’); putchar(’O’); putchar(’V’); putchar(’E’); putchar(’R’); putchar(’H’); putchar(’E’); putchar(’A’); putchar(’T’); putcommand(0xC0);//DD RAM location 1 - line 2 putchar(’R’); putchar(’E’); putchar(’S’); putchar(’E’); putchar(’T’); putchar(’ ’); putchar(’E’); putchar(’N’); putchar(’G’); putchar(’ ’); putchar(’C’); putchar(’B’); putchar(’ ’); putchar(’3’); putchar(’0’); putchar(’S’); } //************************************************************************* //void systems_A_OK(void)

296


//************************************************************************* void systems_A_OK(void) { clear_LCD(); putcommand(0x01); //cursor home putcommand(0x80); //DD RAM location 1 - line 1 putchar(’S’); putchar(’Y’); putchar(’S’); putchar(’T’); putchar(’E’); putchar(’M’); putchar(’S’); putchar(’ ’); putchar(’A’); putchar(’-’); putchar(’O’); putchar(’K’); putchar(’!’); putchar(’!’); putchar(’!’); } //************************************************************************* //void flash_LED_panel(void) //************************************************************************* void flash_LED_panel(void) { flash_panel = YES; flash_timer = 0; PORTB = 0x00; PORTB_LEDs = OFF; } //************************************************************************* //convert_display_voltage_LCD: converts binary weighted voltage to ASCII //representation and prints result to LCD screen //************************************************************************* void convert_display_voltage_LCD(int binary_voltage) { float actual_voltage; //voltage between 0 and 5 volts int all_integer_voltage; //integer representation of voltage //int representation of voltage int hundreths_place, tens_place, ones_place; //char representation of voltage char hundreths_place_char, tens_place_char, ones_place_char;


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// display analog voltage on LCD putcommand(0xC0); //LCD cursor to line 2 //scale float voltage 0..5V actual_voltage = ((float)(binary_voltage)/(float)(0x3FF))*5.0; //voltage represented 0 to 500 all_integer_voltage=actual_voltage * 100;//represent as all integer hundreths_place = all_integer_voltage/100;//isolate first digit hundreths_place_char = (char)(hundreths_place + 48); //convert to ascii putchar(hundreths_place_char); //display first digit putchar(’.’); //print decimal point to LCD //isolate tens place tens_place = (int)((all_integer_voltage - (hundreths_place*100))/10); tens_place_char=(char)(tens_place+48); //convert to ASCII putchar(tens_place_char); //print to LCD //isolate ones place ones_place = (int)((all_integer_voltage - (hundreths_place*100))%10); ones_place_char=(char)(ones_place+48); //convert to ASCII putchar(ones_place_char); //print to LCD putchar(’V’); //print unit V } //************************************************************************* //convert_int_to_string_display_LCD: converts 16 bit to unsigned integer //values range from 0 to 65,535 //prints result to LCD screen //************************************************************************* void convert_int_to_string_display_LCD(unsigned int total_integer_value) { int ten_thousandths_place, thousandths_place; int hundreths_place, tens_place, ones_place; char ten_thousandths_place_char, thousandths_place_char; char hundreths_place_char, tens_place_char, ones_place_char; putcommand(0xC0);

//LCD cursor to line 2 //10,000th place ten_thousandths_place = total_integer_value/10000; ten_thousandths_place_char = (char)(ten_thousandths_place+48); putchar(ten_thousandths_place_char);

298


//1,000th place thousandths_place = (int)((total_integer_value (ten_thousandths_place*10000))/1000); thousandths_place_char = (char)(thousandths_place+48); putchar(thousandths_place_char); //100th place hundreths_place = (int)((total_integer_value (ten_thousandths_place*10000)(thousandths_place*1000))/100); hundreths_place_char = (char)(hundreths_place + 48); putchar(hundreths_place_char); //10th place tens_place = (int)((total_integer_value -(ten_thousandths_place*10000)(thousandths_place*1000)-(hundreths_place*100))/10); tens_place_char=(char)(tens_place+48); //convert to ASCII putchar(tens_place_char); //print to LCD //isolate ones place ones_place = (int)((total_integer_value -(ten_thousandths_place*10000)(thousandths_place*1000)-(hundreths_place*100))%10); ones_place_char=(char)(ones_place+48); //convert to ASCII putchar(ones_place_char); //print to LCD }

//************************************************************************* //end of file: flight_sim.c //*************************************************************************

8.12 EXTENDED EXAMPLE 4: SUBMERSIBLE ROBOT The area of submersible robots is fascinating and challenging. To design a robot is quite complex. To add the additional requirement of waterproofing key components adds an additional level of challenge. (Water and electricity do not mix!) In this section we develop a control system for a remotely operated vehicle, an ROV. By definition an ROV is equipped with a tether umbilical cable that provides power and control signals from a surface support platform. An Autonomous Underwater Vehicle (AUV) carries its own power and control equipment and does not require surface support. We limit our discussion to the development of an Arduino based control system. Details on the construction and waterproofing of an ROV are provided in the excellent and fascinating “Build Your Own Underwater Robot and Other Wet Projects” by Harry Bohm and Vickie Jensen. We

8.12. EXTENDED EXAMPLE 4: SUBMERSIBLE ROBOT

299

power and control umbilical vertical thruster

left float

right float

left thruster

right thruster Figure 8.28: SeaPerch ROV. (Adapted and used with permission of Bohm and Jensen, West Coast Words Publishing.)

develop a control system for the SeaPerch style of ROV as shown in Figure 8.28. There is a national competition for students based on the SeaPerch ROV. The goal of the program is to stimulate interest in the next generation of marine related engineering specialties [seaperch].

8.12.1 REQUIREMENTS The requirements for this system include: • Develop a control system to allow a three motor ROV to move forward, left (port) and right (starboard). • The ROV will be pushed down to a shallow depth via a vertical thruster and return to surface based on its own, slightly positive buoyancy. • ROV movement will be under joystick control.

300

8. ATMEL AVR OPERATING PARAMETERS AND INTERFACING Seaperch Control System

ROV direction

direction five position joystick

motor control

LED assertion

motor assertion

light emitting diodes (LEDs) interface

motor interface

left thruster

vertical thruster

right thruster

left LED

vertical LED

right LED

Figure 8.29: SeaPerch ROV structure chart.

• All power and control circuitry will be maintained in a surface support platform.

8.12.2 STRUCTURE CHART The Sea Perch structure chart is provided in Figure 8.29. As can be seen in the figure, the SeaPerch control system will accept input from the five position joystick (left, right, select, up and down). We will use the joystick shield available from SparkFun Electronics and illustrated in Figure 8.30. The joystick schematic and connections to the Arduino UNO R3 are provided in Figure 8.31. In response to user joystick input, the SeaPerch control algorithm will issue a control command indicating desired ROV direction. In response to this desired direction command, the motor control algorithm will issue control signals to assert the appropriate motors and LEDs.

8.12.3 CIRCUIT DIAGRAM The circuit diagram for the SeaPerch control system is provided in Figure 8.31. The Arduino compatible joystick shield is used to select desired ROV direction. There are three LED interface


301

SW1(D3)

SW4(D5)

SW2(D4)

8 9 10 11 12 13 GND Aref

SW3(D6)

5 4 3 2 Horizontal (A1) - 1 Vertical (A0) - 0 Analog In

RX TX 2 - Select (D2) 3 - SW1(D3) 4 - SW2(D4) 5 - SW4(D5) 6 - SW3(D6) 7

Vertical (analog A0)

Select (D2) (push)

VIN GND GND +5V +3.3V Reset SW5 (Reset)

Horizontal (analog A1)

Figure 8.30: Joystick shield. (Used with permission of SparkFun Electronics.)

circuits connected to digital pins D7, D8 and D9. The prime mover for the ROV will be two waterproofed motors or two bilge pumps. Details on motor waterproofing may be found in “Build Your Own Underwater Robot and Other Wet Projects.” The motors are driven by the pulse width modulation channels (d10 and D11) via power FETs as shown in Figure8.31. Both the LED and the motor interfaces were discussed earlier in the chapter.

8.12.4 UML ACTIVITY DIAGRAM The SeaPerch control system UML activity diagram is provided in Figure 8.32. After initializing ports the control algorithm is placed in a continuous loop awaiting user input. In response to user input, the algorithm determines desired direction of ROV travel and asserts appropriate control signals for the LED and motors.

302


SW1(D3)

SW4(D5)

SW2(D4)

+ left thruster

left LED vertical LED right LED right thruster left thruster

M

IRF3205ZPBF-ND

RX TX 2 - Select (D2) 3 - SW1(D3) 4 - SW2(D4) 5 - SW4(D5) 6 - SW3(D6) 7

10Ω

8 9 10 11 12 13 GND Aref

SW3(D6)

Select (D2) (push)

right thruster

SW5 (Reset)

10Ω

Horizontal (analog A1)

D10

5.0 VDC

5.0 VDC

5.0 VDC

220Ω

220Ω

220Ω

+

+

+ right

vertical

left 10ΚΩ

+

VIN GND GND +5V +3.3V Reset

Vertical (analog A0)

D11

D7

13.6 VDC battery

5 4 3 2 Horizontal (A1) - 1 Vertical (A0) - 0 Analog In

13.6 VDC battery

D8

10ΚΩ

Figure 8.31: SeaPerch ROV interface control.

D9

10ΚΩ

2N2222

M -

IR50SQ100 100V, 5A Schottky diode

IRF3205ZPBF-ND



initialize ports

while(1)

no

bow

joystick asserted yes

port

read joystick position (bow, stern, starboard, port, dive)

no

dive? no

starboard stern

yes

bow?

dive

while bow asserted?

yes

assert left, right thruster assert left, right LED

yes

assert vertical thruster assert vertical LED

no

stern : starboard : port yes

while dive asserted? no

Figure 8.32: SeaPerch ROV UML activity diagram.

303

304


8.12.5 MICROCONTROLLER CODE In this example we use switch 2 (SW2 – D4) to control the left thruster (motor or bilge pump) and switch 4 (SW4 – D5) to control the right thruster motor. This is a simple on/off control. That is, when a specific switch is asserted the motor will be on and the corresponding LED will illuminate. //*********************************************************************** //digital input pins #define left_switch 4 //digital pin - left switch #define right_switch 5 //digital pin - right switch

#define left_LED #define right_LED

#define left_motor #define right_motor int

7 9

//digital output pins //LED indicators //digital pin - left LED //digital pin - right LED

11 10


left_sw_value, right_sw_value;

void setup() { pinMode(left_switch, INPUT); pinMode(right_switch,INPUT);

//switch inputs //configure pin 4 for digital input //configure pin 5 for digital input

pinMode(left_LED, OUTPUT); pinMode(right_LED, OUTPUT);

//LED indicators //configure pin 7 for digital output //configure pin 9 for digital output

pinMode(left_motor, OUTPUT); pinMode(right_motor, OUTPUT); }

//motor outputs - PWM //config pin 11 for digital output //config pin 10 for digital output

void loop() { //read input switches left_sw_value = digitalRead(left_switch);


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right_sw_value = digitalRead(right_switch); //left switch asserted - turn left by asserting right motor if((left_sw_value==HIGH)&&(right_sw_value==LOW)) { digitalWrite(left_LED, LOW); //turn left LED off digitalWrite(left_motor, LOW); //turn left motor off digitalWrite(right_LED, HIGH); //turn right LED on digitalWrite(right_motor, HIGH); //turn right motor on delay(500); //delay 500 ms } //right switch asserted - turn right by asserting left motor if((left_sw_value==LOW)&&(right_sw_value==HIGH)) { digitalWrite(left_LED, HIGH); //turn left LED on digitalWrite(left_motor, HIGH); //turn left motor on digitalWrite(right_LED, LOW); //turn right LED off digitalWrite(right_motor, LOW); //turn right motor off delay(500); //delay 500 ms } //both switches asserted - move ROV forward if((left_sw_value==HIGH)&&(right_sw_value==HIGH)) { digitalWrite(left_LED, HIGH); //turn left LED on digitalWrite(left_motor, HIGH); //turn left motor on digitalWrite(right_LED, HIGH); //turn right LED on digitalWrite(right_motor, HIGH); //turn right motor on delay(500); //delay 500 ms } } //***********************************************************************

8.12.6 PROJECT EXTENSIONS The control system provided above has a set of very basic features. Here are some possible extensions for the system: • Provide adjustable speed control for each motor. This advanced feature requires several modifications including a proportional joystick and pulse width modulation signals to the motor.

306


The joystick features currently in use provides a simple on and off signal. A proportional joystick provides an X (horizontal) and Y (vertical) output DC signal proportional to the joystick deflection on each axis. These signals may be fed to the analog-to-digital converter aboard the Arduino UNO R3. The X and Y signals captured from the joystick may be used to provide a pulse width modulated signal with a duty cycle proportional to deflection. The Arduino shield joystick illustrated in 8.30 is equipped with an analog joystick. The X and Y channel of the joystick is also already connected to the Arduino Analog In channels A0 (vertical) and A1 (horizontal) through the shield printed circuit board connections. Equipping the ROV with this modification is given as an assignment at the end of the chapter. • Provide a powered dive and surface thruster. To provide for a powered dive and surface capability, the ROV must be equipped with a vertical thruster equipped with an H-bridge to allow for motor forward and reversal. This modification is given as an assignment at the end of the chapter. • Left and right thruster reverse. Currently the left and right thrusters may only be powered in one direction. To provide additional maneuverability, the left and right thrusters could be equipped with an H-bridge to allow bi-directional motor control. This modification is given as an assignment at the end of the chapter. • Proportional speed control with bi-directional motor control. Both of these advanced features may be provided by driving the H-bridge circuit with PWM signals. This modification is given as an assignment at the end of the chapter.

8.13 EXTENDED EXAMPLE 5: WEATHER STATION In this project we design a weather station to sense wind direction and ambient temperature. The sensed values will be displayed on an LCD Fahrenheit. The wind direction will also be displayed on LEDs arranged in a circular pattern.

8.13.1 REQUIREMENTS The requirements for this system include: • Design a weather station to sense wind direction and ambient temperature. • Sensed wind direction and temperature will be displayed on an LCD. • Sensed temperature will be displayed in the Fahrenheit temperature scale. • Wind direction will be displayed on LEDs arranged in a circular pattern.

8.13. EXTENDED EXAMPLE 5: WEATHER STATION

307

Weather Station

Wind Direction Display

ADC

ch for conv ADC Initialize

conv data

ReadADC

wind direction weather vane

temp data

LM34 temp sensor

wind direction 74154 4:16 decoder

LED interface

Figure 8.33: Weather station structure chart.

8.13.2 STRUCTURE CHART To begin the design process a structure chart is used to partition the system into definable pieces. We employ a top-down design/bottom-up implementation approach. The structure chart for the weather station is provided in Figure 8.33. The main microcontroller subsystem needed for this project is the ADC system to convert the analog voltage from the LM34 temperature sensor and weather vane into digital signals, and the wind direction display. This display consists of a 74154, 4-to-16 decoder and 16 individual LEDs to display wind direction. The system is partitioned until the lowest level of the structure chart contains “doable” pieces of hardware components or software functions. Data flown is shown on the structure chart as directed arrows.

8.13.3 CIRCUIT DIAGRAM The circuit diagram for the weather station is provided in Figure 8.34.The weather station is equipped with two input sensors: the LM34 to measure temperature and the weather vane to measure wind direction. Both of the sensors provide an analog output that is fed to Analog Input 0 (LM34) and Analog Input 1 (weather vane) of the Arduino UNO R3. The LM34 provides 10 mV output per degree Fahrenheit. The weather vane provides 0 to 5 VDC for 360 degrees of vane rotation. The weather vane must be oriented to a known direction with the output voltage at this direction noted. We assume that 0 VDC corresponds to North and the voltage increases as the vane rotates clockwise to the East. The vane output voltage continues to increase until North is again reached at 5 VDC and then rolls over back to - volts. All other directions are derived from this reference point. An LCD is connected to digital pins [7:0] (PORTD [7:0] of the ATmega328) for data and digital pins 8 and 9 for the enable and command/data control lines (PORTB[1:0] of the ATmega328).

308


There are 16 different LEDs to drive for the wind speed indicator. Rather than use 16 microcontroller pins, the binary value of the LED for illumination is provided to the 74154 4-to-16 decoder. The decoder provides a “one cold” output as determined by the binary code provided by PORTC[5:2] of the ATmega328 (Analog In [5:2] on the Arduino UNO R3). For example, when A16 is provided to the 74154 input, output /Y 10 is asserted low, while all other outputs remain at logic high. The 74154 is from the standard TTL family. It has sufficient current sink capability (IOL = 16 mA) to meet the current requirements of an LED (Vf = 1.5 V DC, If = 15 mA).

8.13.4 UML ACTIVITY DIAGRAMS The UML activity diagram for the main program is provided in Figure 8.35. After initializing the subsystems, the program enters a continuous loop where temperature and wind direction is sensed and displayed on the LCD and the LED display. The system then enters a delay to set how often the temperature and wind direction parameters are updated. We have you construct the individual UML activity diagrams for each function as an end of chapter exercise.

8.13.5 MICROCONTROLLER CODE //include file*************************************************************** #include //function prototypes******************************************************** void initialize_ports(void); void initialize_ADC(void); void temperature_to_LCD(unsigned int ADCValue); unsigned int readADC(unsigned char); void LCD_init(void); void putChar(unsigned char); void putcommand(unsigned char); void display_data(void); void convert_wind_direction(unsigned int); void delay(unsigned int number_of_6_55ms_interrupts); void init_timer0_ovf_interrupt(void); void timer0_interrupt_isr(void); //interrupt handler definition #pragma interrupt_handler timer0_interrupt_isr:17 //door profile data //Global variables****************************************************** unsigned int temperature, wind_direction;


309

RS:command/data

enable data 8

Vcc

data


10K

AND671GST

Vcc = 5 VDC Vcc = 5 V

temperature sensor LM34

220

75 1uF

LED0

Vcc = 5 VDC (24) A(23) B(22) C(21) D(20)

Vcc = 5 V

(1)Y0 (2)Y1 (3)Y2

LED0 LED1 LED2

Vcc = 5 VDC

74154 4:16 decoder

220 LED15

G1

weather vane N

G2

LED0

(12)

E

W LED12

(17)Y15

LED4

LED8

S

Figure 8.34: Circuit diagram for weather station.

LED15

+

+

310



initialize ADC initialize LCD

while(1)

convert temp

convert wind direction

display temp & wind direction on LCD display wind direction on LED

delay(desired_update_time)

Figure 8.35: Weather station UML activity diagram.


unsigned int binary_weighted_voltage_low, binary_weighted_voltage_high; unsigned char dir_tx_data; void main(void) { initialize_ports(); initialize_ADC(); LCD_init(); init_timer0_ovf_interrupt(); while(1) { //temperature data: read -> display -> transmit temperature = readADC(0x00); //Read Temp - LM34 temperature_to_LCD (temperature); //Convert and display temp on LCD //wind direction data: read -> display -> transmit wind_direction = readADC(0x01); //Read wind direction convert_wind_direction(wind_direction); //Convert wind direction //delay 15 minutes delay(13740): } } //*********************************************************************** void { DDRB DDRC DDRD }

initialize_ports() = 0x03; = 0x3c; = 0xFF;

//PORTB[1:0] as outputs //PORTC[5:2] as outputs //PORTD[7:0] as outputs

//*********************************************************************** void initialize_ADC() { ADMUX = 0;

//select channel 0

311

312


ADCSRA = 0xC3; while(!(ADCSRA & 0x10)); ADCSRA |= 0x10; }

//enable ADC and set module enable ADC //set module prescalar to 8 //Wait until conversion is ready //Clear conversion ready flag

//*********************************************************************** unsigned int readADC(unsigned char channel) { unsigned int binary_weighted_voltage, binary_weighted_voltage_low; unsigned int binary_weighted_voltage_high;//weighted binary voltage ADMUX = channel; ADCSRA |= 0x43;

//Select channel //Start conversion //Set ADC module prescalar //to 8 critical for //accurate ADC results while (!(ADCSRA & 0x10)); //Check if conversion is ready ADCSRA |= 0x10; //Clear conv rdy flag set the bit binary_weighted_voltage_low = ADCL; //Read 8 low bits first (important) //Read 2 high bits, multiply by 256 binary_weighted_voltage_high = ((unsigned int)(ADCH << 8)); binary_weighted_voltage=binary_weighted_voltage_low+binary_weighted_voltage_high; return binary_weighted_voltage; //ADCH:ADCL } //*********************************************************************** //LCD_Init: initialization for an LCD connected in the following manner: //LCD: AND671GST 1x16 character display //LCD configured as two 8 character lines in a 1x16 array //LCD data: bus PORTD[7:0] //LCD RS: PORTB[1] //LCD E: PORTB[0] //*********************************************************************** void LCD_init(void) { delay(1);


delay(1); delay(1);

putcommand(0x38); delay(1); putcommand(0x38); delay(1); putcommand(0x38); putcommand(0x38); putcommand(0x0E); putcommand(0x01); putcommand(0x06); putcommand(0x00); putcommand(0x00); }

//output command string to //initialize LCD //function set 8-bit //function set 8-bit //function set 8-bit //one line, 5x7 char //display on //display clear-1.64 ms //entry mode set //clear display, cursor at home //clear display, cursor at home

//*********************************************************************** void putChar(unsigned char c) { DDRD = 0xff; DDRB = DDRB|0x03; PORTD = c; PORTB = PORTB|0x02; PORTB = PORTB|0x01; PORTB = PORTB&0xfe; delay(1); }

//set PORTD as output //make PORTB[1:0] output //RS=1 //E=1 //E=0

//*********************************************************************** void putcommand(unsigned char d) { DDRD = 0xff; DDRB = DDRB|0x03; PORTB = PORTB & 0xfd; PORTD = d;

//set PORTD as output //make PORTB[1:0] output //RS=0

313

314


PORTB = PORTB|0x01; PORTB = PORTB&0xfe; delay(1); }

//E=1 //E=0

//*********************************************************************** void temperature_to_LCD(unsigned int ADCValue) { float voltage,temperature; unsigned int tens, ones, tenths; voltage = (float)ADCValue*5.0/1024.0; temperature = voltage*100;

tens = (unsigned int)(temperature/10); ones = (unsigned int)(temperature-(float)tens*10); tenths = (unsigned int)(((temperature-(float)tens*10)-(float)ones)*10); putcommand(0x01); putcommand(0x80); putChar((unsigned char)(tens)+48); putChar((unsigned char)(ones)+48); putChar(’.’); putChar((unsigned char)(tenths)+48); putChar(’F’); }

//cursor home //DD RAM location 1 - line 1

//*********************************************************************** void convert_wind_direction(unsigned int wind_dir_int) { float wind_dir_float; //convert wind direction to float wind_dir_float = ((float)wind_dir_int)/1024.0) * 5; //N - LED0


if((wind_dir_float <= 0.15625)||(wind_dir_float > 4.84375)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’N’); //LCD displays: N PORTC = 0x00; //illuminate LED 0 } //NNE - LED1 if((wind_dir_float > 0.15625)||(wind_dir_float <= 0.46875)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’N’); //LCD displays: NNE putchar(’N’); putchar(’E’); PORTC = 0x04; //illuminate LED 1 } //NE - LED2 if((wind_dir_float > 0.46875)||(wind_dir_float <= 0.78125)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’N’); //LCD displays: NE putchar(’E’); PORTC = 0x08; //illuminate LED 2 } //ENE - LED3 if((wind_dir_float > 0.78125)||(wind_dir_float <= 1.09375)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’E’); //LCD displays: NNE putchar(’N’); putchar(’E’); PORTC = 0x0c; //illuminate LED 3

315

316


} //E - LED4 if((wind_dir_float > 1.09375)||(wind_dir_float <= 1.40625)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’E’); //LCD displays: E PORTC = 0x10; //illuminate LED 4 } //ESE - LED5 if((wind_dir_float > 1.40625)||(wind_dir_float <= 1.71875)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’E’); //LCD displays: ESE putchar(’S’); putchar(’E’); PORTC = 0x14; //illuminate LED 5 } //SE - LED6 if((wind_dir_float > 1.71875)||(wind_dir_float <= 2.03125)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’S’); //LCD displays: SE putchar(’E’); PORTC = 0x10; //illuminate LED 6 } //SSE - LED7 if((wind_dir_float > 2.03125)||(wind_dir_float <= 2.34875)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2


putchar(’S’); putchar(’S’); putchar(’E’); PORTC = 0x1c; }

//LCD displays: SSE

//illuminate LED 7

//S - LED8 if((wind_dir_float > 2.34875)||(wind_dir_float <= 2.65625)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’S’); //LCD displays: S PORTC = 0x20;

//illuminate LED 8

} //SSW - LED9 if((wind_dir_float > 2.65625)||(wind_dir_float <= 2.96875)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’S’); //LCD displays: SSW putchar(’S’); putchar(’W’); PORTC = 0x24; //illuminate LED 9 } //SW - LED10 (A) if((wind_dir_float > 2.96875)||(wind_dir_float <= 3.28125)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’S’); //LCD displays: SW putchar(’W’); PORTC = 0x28; //illuminate LED 10 (A) }

317

318


//WSW - LED11 (B) if((wind_dir_float > 3.28125)||(wind_dir_float <= 3.59375)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’W’); //LCD displays: WSW putchar(’S’); putchar(’W’); PORTC = 0x2c; //illuminate LED 11 (B) } //W - LED12 (C) if((wind_dir_float > 3.59375)||(wind_dir_float <= 3.90625)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’W’); //LCD displays: W PORTC = 0x30; //illuminate LED 12 (C) } //WNW - LED13 (D) if((wind_dir_float > 3.90625)||(wind_dir_float <= 4.21875)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’W’); //LCD displays: WNW putchar(’N’); putchar(’W’); PORTC = 0x34; //illuminate LED 13 (D) } //NW - LED14 (E) if((wind_dir_float > 4.21875)||(wind_dir_float <= 4.53125)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’N’); //LCD displays: NW putchar(’W’); PORTC = 0x38; //illuminate LED 14 (E)


} //NNW - LED15(F) if((wind_dir_float > 4.53125)||(wind_dir_float < 4.84375)) { putcommand(0x01); //cursor to home putcommand(0xc0); //DD RAM location 1 - line 2 putchar(’N’); //LCD displays: NNW putchar(’N’); putchar(’W’); PORTC = 0x3c; //illuminate LED 15 (F) } } //*********************************************************************** //delay(unsigned int num_of_65_5ms_interrupts): this generic delay //function provides the specified delay as the number of 65.5 ms "clock //ticks" from the Timer0 interrupt. //Note: this function is only valid when using a 1 MHz crystal or ceramic // resonator. Function time constants need to be adjusted for other // values of the timebase. //*********************************************************************** void delay(unsigned int number_of_65_5ms_interrupts) { TCNT0 = 0x00; //reset timer0 delay_timer = 0; while(delay_timer <= number_of_65_5ms_interrupts) { ; } } //*********************************************************************** //int_timer0_ovf_interrupt(): The Timer0 overflow interrupt is being //employed as a time base for a master timer for this project. //The internal time base is set to operate at 1 MHz and then //is divided by 256. The 8-bit Timer0 register (TCNT0) overflows

319

320


//every 256 counts or every 65.5 ms. //*********************************************************************** void init_timer0_ovf_interrupt(void) { TCCR0 = 0x04; //div timer0 timebase by 256, overfl. occurs every 65.5ms TIMSK = 0x01; //enable timer0 overflow interrupt asm("SEI"); //enable global interrupt } //*********************************************************************** //timer0_interrupt_isr: //Note: Timer overflow 0 is cleared by hardware when executing the //corresponding interrupt handling vector. //*********************************************************************** void timer0_interrupt_isr(void) { input_delay++; }

//input delay processing

//***********************************************************************

8.14 SUMMARY In this chapter, we discussed the voltage and current operating parameters for the Arduino UNO R3 processing board and the Atmel ATmega328 microcontroller. We discussed how this information may be applied to properly design an interface for common input and output circuits. It must be emphasized a properly designed interface allows the microcontroller to operate properly within its parameter envelope. If due to a poor interface design, a microcontroller is used outside its prescribed operating parameter values, spurious and incorrect logic values will result. We provided interface information for a wide range of input and output devices. We also discussed the concept of interfacing a motor to a microcontroller using PWM techniques coupled with high power MOSFET or SSR switching devices. We closed the chapter with a number of extended examples.

8.15 REFERENCES • Pack D, Barrett S (2002) 68HC12 Microcontroller: Theory and Applications. Prentice-Hall Incorporated, Upper Saddle River, NJ.


321

• Barrett S, Pack D (2004) Embedded Systems Design with the 68HC12 and HCS12. PrenticeHall Incorporated, Upper Saddle River, NJ. • Crydom Corporation, 2320 Paseo de las Americas, Suite 201, San Diego, CA (www.crydom. com). • Sick/Stegmann Incorporated, Dayton, OH, (www.stegmann.com). • Images Company, 39 Seneca Loop, Staten Island, NY 10314. • Atmel 8-bit AVR Microcontroller with 16/32/64K Bytes In-System Programmable Flash, ATmega328P/V, ATmega324P/V, 644P/V data sheet: 8011I-AVR-05/08, Atmel Corporation, 2325 Orchard Parkway, San Jose, CA 95131. • Barrett S, Pack D (2006) Microcontrollers Fundamentals for Engineers and Scientists. Morgan and Claypool Publishers. DOI: 10.2200/S00025ED1V01Y200605DCS001 • Barrett S and Pack D (2008) Atmel AVR Microcontroller Primer Programming and Interfacing. Morgan and Claypool Publishers. DOI: 10.2200/S00100ED1V01Y200712DCS015 • Barrett S (2010) Embedded Systems Design with the Atmel AVR Microcontroller. Morgan and Claypool Publishers. DOI: 10.2200/S00225ED1V01Y200910DCS025 • National Semiconductor, LM34/LM34A/LM34C/LM34CA/LM34D Precision Fahrenheit Temperature Sensor, 1995. • Bohm H and Jensen V (1997) Build Your Own Underwater Robot and Other Wet Projects. Westcoast Words. • seaperch, www.seaperch.org • SparkFun, www.sparkfun.com • Pack D and Barrett S (2011) Microcontroller Programming and Interfacing Texas Instruments MSP430. Morgan and Claypool Publishers.

8.16 CHAPTER PROBLEMS 1. What will happen if a microcontroller is used outside of its prescribed operating envelope? 2. Discuss the difference between the terms “sink” and “source” as related to current loading of a microcontroller. 3. Can an LED with a series limiting resistor be directly driven by the Atmel microcontroller? Explain.

322


4. In your own words, provide a brief description of each of the microcontroller electrical parameters. 5. What is switch bounce? Describe two techniques to minimize switch bounce. 6. Describe a method of debouncing a keypad. 7. What is the difference between an incremental encoder and an absolute encoder? Describe applications for each type. 8. What must be the current rating of the 2N2222 and 2N2907 transistors used in the tri-state LED circuit? Support your answer. 9. Draw the circuit for a six character seven segment display. Fully specify all components. Write a program to display “ATmega328.” 10. Repeat the question above for a dot matrix display. 11. Repeat the question above for a LCD display. 12. What is the difference between a unipolar and bipolar stepper motor? 13. What controls the speed of rotation of a stepper motor? 14. A stepper motor provides and angular displacement of 1.8 degrees per step. How can this resolution be improved? 15. Write a function to convert an ASCII numeral representation (0 to 9) to a seven segment display. 16. Why is an interface required between a microcontroller and a stepper motor? 17. For the SeaPerch ROV provide adjustable speed control for each motor. This advanced feature requires several modifications including a proportional joystick and pulse width modulation signals to the motor. The joystick currently in use provides a simple on and off signal. A proportional joystick provides an X and Y output DC signal proportional to the joystick deflection on each axis. These signals may be fed to the analog-to-digital converter aboard the Arduino UNO R3. The X and Y signals captured from the joystick may be used to provide a pulse width modulated signal with a duty cycle proportional to deflection. 18. For the SeaPerch ROV provide a powered dive and surface thruster. To provide for a powered dive and surface capability, the ROV must be equipped with a vertical thruster equipped with an H-bridge to allow for motor forward and reversal.


323

19. For the SeaPerch ROV provide left and right thruster reverse. Currently the left and right thrusters may only be powered in one direction. To provide additional maneuverability, the left and right thrusters could be equipped with an H-bridge to allow bi-directional motor control. 20. For the SeaPerch ROV provide proportional speed control with bi-directional motor control. Both of these advanced features may be provided by driving the H-bridge circuit with PWM signals. 21. Construct the UML activity diagrams for all functions related to the weather station. 22. It is desired to updated weather parameters every 15 minutes. Write a function to provide a 15 minute delay. 23. Add one of the following sensors to the weather station: • anemometer • barometer • hygrometer • rain gauge • thermocouple You will need to investigate background information on the selected sensor, develop an interface circuit for the sensor, and modify the weather station code. 24. Modify the weather station software to also employ a 138 x 110 LCD. Display pertinent weather data on the display. 25. Equip the weather station with an MMC/SD flash memory card. 26. Modify the motor speed control circuit interface to provide for bi-directional motor control. 27. Use optical encoder output channels A and B to determine motor direction and speed. 28. Modify the motor speed control algorithm to display motor direction (CW or CCW) and speed in RPM on the LCD. 29. The Blinky 602A robot under microcontroller control abruptly starts and stops when PWM is applied. Modify the algorithm to provide the capability to gradually ramp up (and down) the motor speed. 30. Modify the Blinky 602A circuit and microcontroller code such that the maximum speed of the robot is set with an external potentiometer.

324


31. Modify the Blinky 602A circuit and microcontroller code such that the IR sensors are only asserted just before a range reading is taken. 32. Apply embedded system design techniques presented throughout the text to a project of your choosing. Follow the design process and provide the following products: • system description, • system requirements, • a structure chart, • system circuit diagram, • UML activity diagrams, and the • microcontroller code. 33. Add the following features to the Blinky 602A platform: • Line following capability (Hint: Adapt the line following circuitry onboard the Blinky 602A to operate with the MSP430.) • Two way robot communications (use the IR sensors already aboard) • LCD display for status and troubleshooting display • Voice output (Hint: Use an ISD 4003 Chip Corder.) 34. Develop an embedded system controlled submarine (www.seaperch.org). 35. Equip the Arduino UNO R3 with automatic cell phone dialing capability to notify you when a fire is present in your home. 36. Develop an embedded www.rctoys.com).

system

controlled

dirigible/blimp

(www.microflight.com,

37. Develop a trip odometer for your bicycle (Hint: use a Hall Effect sensor to detect tire rotation). 38. Develop a timing system for a 4 lane pinewood derby track. 39. Develop a playing board and control system for your favorite game (Yahtzee, Connect Four, Battleship, etc.). 40. You have a very enthusiastic dog that loves to chase balls. Develop a system to launch balls for the dog.

325

APPENDIX

A

ATmega328 Register Set

Figure A.1: Atmel AVR ATmega328 Register Set. (Figure used with permission of Atmel, Incorporated.)

326

A. ATMEGA328 REGISTER SET


327


328

A. ATMEGA328 REGISTER SET


329

APPENDIX

B

ATmega328 Header File During C programming, the contents of a specific register may be referred to by name when an appropriate header file is included within your program. The header file provides the link between the register name used within a program and the hardware location of the register. Provided below is the ATmega328 header file from the ICC AVR compiler. This header file was provided courtesy of ImageCraft Incorporated. #ifndef __iom328pv_h #define __iom328pv_h /* ATmega328P header file for * ImageCraft ICCAVR compiler */ /* i/o register addresses * >= 0x60 are memory mapped only */ /* 2006/10/01 created */ /* Port #define #define #define

D */ PIND DDRD PORTD

(*(volatile unsigned char *)0x29) (*(volatile unsigned char *)0x2A) (*(volatile unsigned char *)0x2B)

/* Port #define #define #define

C */ PINC DDRC PORTC

(*(volatile unsigned char *)0x26) (*(volatile unsigned char *)0x27) (*(volatile unsigned char *)0x28)


B */ PINB DDRB PORTB


330

B. ATMEGA328 HEADER FILE


A */ PINA DDRA PORTA


/* Timer/Counter Interrupts #define TIFR0 (*(volatile #define OCF0B 2 #define OCF0A 1 #define TOV0 0 #define TIMSK0 (*(volatile #define OCIE0B 2 #define OCIE0A 1 #define TOIE0 0 #define TIFR1 (*(volatile #define ICF1 5 #define OCF1B 2 #define OCF1A 1 #define TOV1 0 #define TIMSK1 (*(volatile #define ICIE1 5 #define OCIE1B 2 #define OCIE1A 1 #define TOIE1 0 #define TIFR2 (*(volatile #define OCF2B 2 #define OCF2A 1 #define TOV2 0 #define TIMSK2 (*(volatile #define OCIE2B 2 #define OCIE2A 1 #define TOIE2 0

*/ unsigned char *)0x35)

unsigned char *)0x6E)

unsigned char *)0x36)

unsigned char *)0x6F)



/* External Interrupts */ #define EIFR (*(volatile unsigned char *)0x3C) #define INTF2 2 #define INTF1 1 #define INTF0 0

331

#define EIMSK #define INT2 #define INT1 #define INT0 #define EICRA #define ISC21 #define ISC20 #define ISC11 #define ISC10 #define ISC01 #define ISC00

(*(volatile unsigned char *)0x3D) 2 1 0 (*(volatile unsigned char *)0x69) 5 4 3 2 1 0

/* Pin Change Interrupts */ #define PCIFR (*(volatile #define PCIF3 3 #define PCIF2 2 #define PCIF1 1 #define PCIF0 0 #define PCICR (*(volatile #define PCIE3 3 #define PCIE2 2 #define PCIE1 1 #define PCIE0 0 #define PCMSK0 (*(volatile #define PCMSK1 (*(volatile #define PCMSK2 (*(volatile #define PCMSK3 (*(volatile

unsigned char *)0x3B)


unsigned unsigned unsigned unsigned

char char char char

*)0x6B) *)0x6C) *)0x6D) *)0x73)

/* GPIOR */ #define GPIOR0 #define GPIOR1 #define GPIOR2

(*(volatile unsigned char *)0x3E) (*(volatile unsigned char *)0x4A) (*(volatile unsigned char *)0x4B)

/* EEPROM */ #define EECR #define EEPM1 #define EEPM0 #define EERIE #define EEMPE

(*(volatile unsigned char *)0x3F) 5 4 3 2

332


#define #define #define #define #define #define #define #define

EEMWE EEPE EEWE EERE EEDR EEAR EEARL EEARH

2 1 1 0 (*(volatile (*(volatile (*(volatile (*(volatile


char *)0x40) int *)0x41) char *)0x41) char *)0x42)

/* GTCCR */ #define GTCCR (*(volatile unsigned char *)0x43) #define TSM 7 #define PSRASY 1 #define PSR2 1 #define PSRSYNC 0 #define PSR10 0 /* Timer/Counter 0 */ #define OCR0B (*(volatile #define OCR0A (*(volatile #define TCNT0 (*(volatile #define TCCR0B (*(volatile #define FOC0A 7 #define FOC0B 6 #define WGM02 3 #define CS02 2 #define CS01 1 #define CS00 0 #define TCCR0A (*(volatile #define COM0A1 7 #define COM0A0 6 #define COM0B1 5 #define COM0B0 4 #define WGM01 1 #define WGM00 0 /* SPI */ #define SPCR #define SPIE


char char char char

*)0x48) *)0x47) *)0x46) *)0x45)


(*(volatile unsigned char *)0x4C) 7

333

#define SPE #define DORD #define MSTR #define CPOL #define CPHA #define SPR1 #define SPR0 #define SPSR #define SPIF #define WCOL #define SPI2X #define SPDR

6 5 4 3 2 1 0 (*(volatile unsigned char *)0x4D) 7 6 0 (*(volatile unsigned char *)0x4E)

/* Analog Comparator Control and Status Register */ #define ACSR (*(volatile unsigned char *)0x50) #define ACD 7 #define ACBG 6 #define ACO 5 #define ACI 4 #define ACIE 3 #define ACIC 2 #define ACIS1 1 #define ACIS0 0 /* OCDR */ #define OCDR #define IDRD

(*(volatile unsigned char *)0x51) 7

/* MCU */ #define MCUSR #define JTRF #define WDRF #define BORF #define EXTRF #define PORF #define MCUCR #define JTD #define PUD #define IVSEL

(*(volatile unsigned char *)0x54) 4 3 2 1 0 (*(volatile unsigned char *)0x55) 7 4 1

334


#define

IVCE

#define SMCR #define SM2 #define SM1 #define SM0 #define SE

0 (*(volatile unsigned char *)0x53) 3 2 1 0

/* SPM Control and Status Register */ #define SPMCSR (*(volatile unsigned char *)0x57) #define SPMIE 7 #define RWWSB 6 #define SIGRD 5 #define RWWSRE 4 #define BLBSET 3 #define PGWRT 2 #define PGERS 1 #define SPMEN 0 /* Stack Pointer */ #define SP (*(volatile unsigned int *)0x5D) #define SPL (*(volatile unsigned char *)0x5D) #define SPH (*(volatile unsigned char *)0x5E) /* Status REGister */ #define SREG (*(volatile unsigned char *)0x5F) /* Watchdog Timer Control Register */ #define WDTCSR (*(volatile unsigned char *)0x60) #define WDTCR (*(volatile unsigned char *)0x60) #define WDIF 7 #define WDIE 6 #define WDP3 5 #define WDCE 4 #define WDE 3 #define WDP2 2 #define WDP1 1 #define WDP0 0

335

/* clock prescaler control register */ #define CLKPR (*(volatile unsigned char *)0x61) #define CLKPCE 7 #define CLKPS3 3 #define CLKPS2 2 #define CLKPS1 1 #define CLKPS0 0 /* PRR */ #define PRR0 (*(volatile unsigned char *)0x64) #define PRTWI 7 #define PRTIM2 6 #define PRTIM0 5 #define PRUSART1 4 #define PRTIM1 3 #define PRSPI 2 #define PRUSART0 1 #define PRADC 0 /* Oscillator Calibration Register */ #define OSCCAL (*(volatile unsigned char *)0x66) /* ADC */ #define ADC #define ADCL #define ADCH #define ADCSRA #define ADEN #define ADSC #define ADATE #define ADIF #define ADIE #define ADPS2 #define ADPS1 #define ADPS0 #define ADCSRB #define ACME #define ADTS2 #define ADTS1

(*(volatile (*(volatile (*(volatile (*(volatile 7 6 5 4 3 2 1 0 (*(volatile 6 2 1


int *)0x78) char *)0x78) char *)0x79) char *)0x7A)

unsigned char *)0x7B)

336


#define ADTS0 #define ADMUX #define REFS1 #define REFS0 #define ADLAR #define MUX4 #define MUX3 #define MUX2 #define MUX1 #define MUX0

0 (*(volatile unsigned char *)0x7C) 7 6 5 4 3 2 1 0

/* DIDR */ #define DIDR0 #define ADC7D #define ADC6D #define ADC5D #define ADC4D #define ADC3D #define ADC2D #define ADC1D #define ADC0D #define DIDR1 #define AIN1D #define AIN0D

(*(volatile unsigned char *)0x7E) 7 6 5 4 3 2 1 0 (*(volatile unsigned char *)0x7F) 1 0

/* Timer/Counter1 */ #define ICR1 (*(volatile #define ICR1L (*(volatile #define ICR1H (*(volatile #define OCR1B (*(volatile #define OCR1BL (*(volatile #define OCR1BH (*(volatile #define OCR1A (*(volatile #define OCR1AL (*(volatile #define OCR1AH (*(volatile #define TCNT1 (*(volatile #define TCNT1L (*(volatile #define TCNT1H (*(volatile #define TCCR1C (*(volatile

unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned unsigned

int *)0x86) char *)0x86) char *)0x87) int *)0x8A) char *)0x8A) char *)0x8B) int *)0x88) char *)0x88) char *)0x89) int *)0x84) char *)0x84) char *)0x85) char *)0x82)

337

#define FOC1A 7 #define FOC1B 6 #define TCCR1B (*(volatile unsigned char *)0x81) #define ICNC1 7 #define ICES1 6 #define WGM13 4 #define WGM12 3 #define CS12 2 #define CS11 1 #define CS10 0 #define TCCR1A (*(volatile unsigned char *)0x80) #define COM1A1 7 #define COM1A0 6 #define COM1B1 5 #define COM1B0 4 #define WGM11 1 #define WGM10 0 /* Timer/Counter2 */ #define ASSR (*(volatile #define EXCLK 6 #define AS2 5 #define TCN2UB 4 #define OCR2AUB 3 #define OCR2BUB 2 #define TCR2AUB 1 #define TCR2BUB 0 #define OCR2B (*(volatile #define OCR2A (*(volatile #define TCNT2 (*(volatile #define TCCR2B (*(volatile #define FOC2A 7 #define FOC2B 6 #define WGM22 3 #define CS22 2 #define CS21 1 #define CS20 0 #define TCCR2A (*(volatile #define COM2A1 7

unsigned char *)0xB6)


char char char char

*)0xB4) *)0xB3) *)0xB2) *)0xB1)

unsigned char *)0xB0)

338


#define #define #define #define #define

COM2A0 COM2B1 COM2B0 WGM21 WGM20

/* 2-wire SI */ #define TWBR #define TWSR #define TWPS1 #define TWPS0 #define TWAR #define TWGCE #define TWDR #define TWCR #define TWINT #define TWEA #define TWSTA #define TWSTO #define TWWC #define TWEN #define TWIE #define TWAMR

6 5 4 1 0

(*(volatile (*(volatile 1 0 (*(volatile 0 (*(volatile (*(volatile 7 6 5 4 3 2 0 (*(volatile

/* USART0 */ #define UBRR0H (*(volatile #define UBRR0L (*(volatile #define UBRR0 (*(volatile #define UCSR0C (*(volatile #define UMSEL01 7 #define UMSEL00 6 #define UPM01 5 #define UPM00 4 #define USBS0 3 #define UCSZ01 2 #define UCSZ00 1 #define UCPOL0 0 #define UCSR0B (*(volatile #define RXCIE0 7

unsigned char *)0xB8) unsigned char *)0xB9)

unsigned char *)0xBA) unsigned char *)0xBB) unsigned char *)0xBC)

unsigned char *)0xBD)


char *)0xC5) char *)0xC4) int *)0xC4) char *)0xC2)

unsigned char *)0xC1)

339

#define TXCIE0 6 #define UDRIE0 5 #define RXEN0 4 #define TXEN0 3 #define UCSZ02 2 #define RXB80 1 #define TXB80 0 #define UCSR0A (*(volatile unsigned char *)0xC0) #define RXC0 7 #define TXC0 6 #define UDRE0 5 #define FE0 4 #define DOR0 3 #define UPE0 2 #define U2X0 1 #define MPCM0 0 #define UDR0 (*(volatile unsigned char *)0xC6) /* USART1 */ #define UBRR1H (*(volatile #define UBRR1L (*(volatile #define UBRR1 (*(volatile #define UCSR1C (*(volatile #define UMSEL11 7 #define UMSEL10 6 #define UPM11 5 #define UPM10 4 #define USBS1 3 #define UCSZ11 2 #define UCSZ10 1 #define UCPOL1 0 #define UCSR1B (*(volatile #define RXCIE1 7 #define TXCIE1 6 #define UDRIE1 5 #define RXEN1 4 #define TXEN1 3 #define UCSZ12 2 #define RXB81 1


char *)0xCD) char *)0xCC) int *)0xCC) char *)0xCA)

unsigned char *)0xC9)

340


#define TXB81 #define UCSR1A #define RXC1 #define TXC1 #define UDRE1 #define FE1 #define DOR1 #define UPE1 #define U2X1 #define MPCM1 #define UDR1

0 (*(volatile unsigned char *)0xC8) 7 6 5 4 3 2 1 0 (*(volatile unsigned char *)0xCE)

/* bits */ /* Port A */ #define PORTA7 #define PORTA6 #define PORTA5 #define PORTA4 #define PORTA3 #define PORTA2 #define PORTA1 #define PORTA0 #define PA7 #define PA6 #define PA5 #define PA4 #define PA3 #define PA2 #define PA1 #define PA0 #define DDA7 #define DDA6 #define DDA5 #define DDA4 #define DDA3 #define DDA2 #define DDA1

7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1

341

#define #define #define #define #define #define #define #define #define

DDA0 PINA7 PINA6 PINA5 PINA4 PINA3 PINA2 PINA1 PINA0

/* Port B */ #define PORTB7 #define PORTB6 #define PORTB5 #define PORTB4 #define PORTB3 #define PORTB2 #define PORTB1 #define PORTB0 #define PB7 #define PB6 #define PB5 #define PB4 #define PB3 #define PB2 #define PB1 #define PB0 #define DDB7 #define DDB6 #define DDB5 #define DDB4 #define DDB3 #define DDB2 #define DDB1 #define DDB0 #define PINB7 #define PINB6 #define PINB5 #define PINB4

0 7 6 5 4 3 2 1 0

7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4

342


#define #define #define #define

PINB3 PINB2 PINB1 PINB0

/* Port C */ #define PORTC7 #define PORTC6 #define PORTC5 #define PORTC4 #define PORTC3 #define PORTC2 #define PORTC1 #define PORTC0 #define PC7 #define PC6 #define PC5 #define PC4 #define PC3 #define PC2 #define PC1 #define PC0 #define DDC7 #define DDC6 #define DDC5 #define DDC4 #define DDC3 #define DDC2 #define DDC1 #define DDC0 #define PINC7 #define PINC6 #define PINC5 #define PINC4 #define PINC3 #define PINC2 #define PINC1 #define PINC0

3 2 1 0

7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0

343

/* Port D */ #define PORTD7 #define PORTD6 #define PORTD5 #define PORTD4 #define PORTD3 #define PORTD2 #define PORTD1 #define PORTD0 #define PD7 #define PD6 #define PD5 #define PD4 #define PD3 #define PD2 #define PD1 #define PD0 #define DDD7 #define DDD6 #define DDD5 #define DDD4 #define DDD3 #define DDD2 #define DDD1 #define DDD0 #define PIND7 #define PIND6 #define PIND5 #define PIND4 #define PIND3 #define PIND2 #define PIND1 #define PIND0

7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0

/* PCMSK3 */ #define PCINT31 #define PCINT30 #define PCINT29 #define PCINT28

7 6 5 4

344


#define PCINT27 #define PCINT26 #define PCINT25 #define PCINT24 /* PCMSK2 */ #define PCINT23 #define PCINT22 #define PCINT21 #define PCINT20 #define PCINT19 #define PCINT18 #define PCINT17 #define PCINT16 /* PCMSK1 */ #define PCINT15 #define PCINT14 #define PCINT13 #define PCINT12 #define PCINT11 #define PCINT10 #define PCINT9 #define PCINT8 /* PCMSK0 */ #define PCINT7 #define PCINT6 #define PCINT5 #define PCINT4 #define PCINT3 #define PCINT2 #define PCINT1 #define PCINT0

3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0 7 6 5 4 3 2 1 0

/* Lock and Fuse Bits with LPM/SPM instructions */ /* lock bits */ #define BLB12 #define BLB11 #define BLB02

5 4 3

345

#define #define #define

BLB01 LB2 LB1

2 1 0

/* fuses #define #define #define #define #define #define #define #define

low bits CKDIV8 CKOUT SUT1 SUT0 CKSEL3 CKSEL2 CKSEL1 CKSEL0

*/ 7 6 5 4 3 2 1 0

/* fuses #define #define #define #define #define #define #define #define

high bits */ OCDEN 7 JTAGEN 6 SPIEN 5 WDTON 4 EESAVE 3 BOOTSZ1 2 BOOTSZ0 1 BOOTRST 0

/* extended fuses */ #define BODLEVEL2 2 #define BODLEVEL1 1 #define BODLEVEL0 0

/* Interrupt Vector Numbers */ #define #define #define #define #define #define #define

iv_RESET iv_INT0 iv_EXT_INT0 iv_INT1 iv_EXT_INT1 iv_INT2 iv_EXT_INT2

1 2 2 3 3 4 4

346


#define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define #define

iv_PCINT0 iv_PCINT1 iv_PCINT2 iv_PCINT3 iv_WDT iv_TIMER2_COMPA iv_TIMER2_COMPB iv_TIMER2_OVF iv_TIM2_COMPA iv_TIM2_COMPB iv_TIM2_OVF iv_TIMER1_CAPT iv_TIMER1_COMPA iv_TIMER1_COMPB iv_TIMER1_OVF iv_TIM1_CAPT iv_TIM1_COMPA iv_TIM1_COMPB iv_TIM1_OVF iv_TIMER0_COMPA iv_TIMER0_COMPB iv_TIMER0_OVF iv_TIM0_COMPA iv_TIM0_COMPB iv_TIM0_OVF iv_SPI_STC iv_USART0_RX iv_USART0_RXC iv_USART0_DRE iv_USART0_UDRE iv_USART0_TX iv_USART0_TXC iv_ANA_COMP iv_ANALOG_COMP iv_ADC iv_EE_RDY iv_EE_READY iv_TWI iv_TWSI

5 6 7 8 9 10 11 12 10 11 12 13 14 15 16 13 14 15 16 17 18 19 17 18 19 20 21 21 22 22 23 23 24 24 25 26 26 27 27

347

#define #define #define #define #define #define #define #define /* */ #endif

iv_SPM_RDY iv_SPM_READY iv_USART1_RX iv_USART1_RXC iv_USART1_DRE iv_USART1_UDRE iv_USART1_TX iv_USART1_TXC

28 28 29 29 30 30 31 31

349

Author’s Biography STEVEN F. BARRETT Steven F. Barrett, Ph.D., P.E., received the BS Electronic Engineering Technology from the University of Nebraska at Omaha in 1979, the M.E.E.E. from the University of Idaho at Moscow in 1986, and the Ph.D. from The University of Texas at Austin in 1993. He was formally an active duty faculty member at the United States Air Force Academy, Colorado and is now the Associate Dean of Academic Programs at the University of Wyoming. He is a member of IEEE (senior) and Tau Beta Pi (chief faculty advisor). His research interests include digital and analog image processing, computer-assisted laser surgery, and embedded controller systems. He is a registered Professional Engineer in Wyoming and Colorado. He co-wrote with Dr. Daniel Pack six textbooks on microcontrollers and embedded systems. In 2004, Barrett was named “Wyoming Professor of the Year” by the Carnegie Foundation for the Advancement of Teaching and in 2008 was the recipient of the National Society of Professional Engineers (NSPE) Professional Engineers in Higher Education, Engineering Education Excellence Award.

351

Index AC device control, 256 AC interfacing, 256 ADC block diagram, 111 ADC conversion, 99 ADC process, 103 ADC registers, 111 analog sensor, 226 anti-aliasing filter, 100 Arduino concept, 1 Arduino Development Environment, 23, 41 Arduino schematic, 9 Arduino shield, 9 Arduino software, 2 Arduino team, 1 Arduino UNO R3, 2 Arduino-based platforms, 9 arithmetic operations, 34 ASCII, 77 ATmega328 ADC, 109 ATmega328 interrupt system, 142 ATmega328 timers, 182 ATmega328 timing system, 173 Atmel ATmega328, 4 background research, 54 battery capacity, 215 battery operation, 215 Baud rate, 76 Bell Laboratory, 100 bit twiddling, 36 Blinky 602A robot, 4, 44

bottom up approach, 58 byte-addressable EEPROM, 15 Closer to the Sun, 49 code re-use, 59 Comfile Technology, 92 comments, 26 counting events, 179 CTC timer mode, 186 current sink, 213 current source, 213 DAC converter, 130 data rate, 103 DC motor, 245 DC motor control, 245 DC motor speed control, 181 decibel (dB), 103 design, 56 design process, 54 digital sensor, 224 documentation, 59 dot matrix display, 233 duty cycle, 174 dynamic range, 103 elapsed time, 177 electrical specifications, 212 embedded system, 54 encoding, 101 external interrupts, 145 fan cooling system, 258

352

INDEX

fast PWM timer mode, 186 Flash EEPROM, 15 flight simulator panel, 272 foreground and background processing, 153 frequency measurement, 179 full duplex, 76 function body, 29 function call, 29 function prototypes, 28 functions, 27 H-bridge, 247 Harry Nyquist, 100 HC CMOS, 212 ideal op amp, 106 if-else, 31, 39 ImageCraft ICC AVR compiler, 144 include files, 27 input capture, 178 input capture programming, 201 input devices, 215 internal interrupt, 148 interrupt handler, 31 interrupt theory, 141 interrupt vector table, 144 ISR, 141 Jonathan Barrettt, 49 joystick, 300 keypad, 219 Lac Laronge, Saskatchewan, 49 LED biasing, 227 light emitting diode (LED), 227 liquid crystal display (LCD), 233 logical operations, 35 loop, 37 main program, 32

MAX232, 77 memory, ATmega328, 14 MOSFET, 243 motor operating parameters, 246 normal timer mode, 184 NRZ format, 77 Nyquist sampling rate, 100 op amp, 106 operating parameters, 211 operational amplifier, 105 operator size, 31 operators, 32 optical encoder, 224 output compare, 180 output device, 226 output timer, 176 parity, 77 period, 174 phase correct timer mode, 186 photodiode, 105 port system, 15 power supply, 2 pre-design, 56 preliminary testing, 58 program constants, 30 program constructs, 36 project description, 54 prototyping, 58 pullup resistors, 217 PWM, 180 PWM programming, 200 quantization, 100 RAM, 15 real time clock, 153 resolution, 102

INDEX

ROV, 298 RS-232, 77 sampling, 100 SeaPerch ROV, 299 sensors, 224 serial communications, 76 servo motor, 203, 245 seven segment displays, 228 Sharp GP12D IR sensor, 4 signal conditioning, 104 signal generation, 180 sketch, 43 sketchbook, 42 solenoid, 244 solid state relay (SSR), 244 sonalert, 256 SPI, 87 stepper motor, 245, 248 STK500, 95 submersible robot, 298 successive-approximation ADC, 109 switch, 40 switch debouncing, 217 switch interface, 217 switches, 215 test plan, 58

353

threshold detector, 129 time base, 17, 174 Timer 0, 182 Timer 1, 189 Timer 2, 193 timer applications, 178 timer modes, 184 timer system programming, 198 timing system, 173 top down approach, 58 top-down design, bottom-up implementation, 57 transducer interface, 104 tri-state LED indicator, 231 TWI, 92 UML, 57 UML activity diagram, 8, 57 Unified Modeling Language (UML), 56 USART, 77 USB-to-serial converter, 3 variables, 31 vibrating motor, 258 volatile, 15 while, 37

Arduino projects

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